Air Quality and Environmental Pollution: First Principles - PDF

GGES3005 & GGES6009 Air Quality and Environmental Pollution First Principles "“Air pollution is now so bad it takes your breath away.” Friends of the Earth newspaper advertisement, 1995. 1.1 Introduction Our Earth is uniquely gifted with an envelope of chemicals that enables life supporting activi...

GGES3005 & GGES6009 Air Quality and Environmental Pollution First Principles "“Air pollution is now so bad it takes your breath away.” Friends of the Earth newspaper advertisement, 1995. 1.1 Introduction Our Earth is uniquely gifted with an envelope of chemicals that enables life supporting activities - commonly known as ‘air’. At least 3000 different chemicals have been identified in air samples. However, it can safely be assumed that the sum total of these chemicals is at least equal to those that have been originally produced on the Earth, plus additional ones formed by their subsequent reactions. Air pollution can be defined as ‘the presence of substances in the atmosphere that cause adverse effects to man and the environment’ It is a term used to describe any unwanted chemicals or other materials that contaminate the air that we breathe resulting in the reduction of air quality. In principle, an air pollutant is any chemical species that exceeds the concentrations or characteristics of the natural constituents of air. However, strictly speaking, a pollutant is defined as a substance that is potentially harmful to the health or well-being of human, animal or plant life, or to the ecological systems. Pollution (in the general sense) was defined in the Tenth Report of the Royal Commission on Environmental Pollution as: ‘The introduction by man into the environment of substances or energy liable to cause hazard to human health, harm to living resources and ecological systems, damage to structure or amenity or interference with legitimate use of the environment.’ This is a very broad definition, and includes many types of pollution that we shall not cover in this book, yet it contains some important ideas. Note that by this definition, chemicals such as sulphur dioxide from volcanoes or methane from the decay of natural vegetation are not counted as pollution, but sulphur dioxide from coal-burning or methane from rice-growing are pollution. Radon, a radioactive gas that is a significant natural hazard in some granitic areas, is not regarded as pollution since it does not arise from people’s activities. The boundaries become fuzzier when we are dealing with natural emissions that are influenced by our actions – for example, there are completely natural biogenic emissions of terpenes1 from forests, and our activities in changing the local patterns of land use have an indirect effect on these emissions. Air pollution is the solid, liquid or gaseous material emitted into the air from stationary or mobile sources, moving subsequently through an aerial path, and perhaps being involved in chemical or physical transformations before eventually being returned to the surface. The material has to interact with something before it can have any environmental impacts. This interaction may be, for example, with other molecules in the atmosphere (photochemical formation of ozone from hydrocarbons), with electromagnetic radiation (by greenhouse gas molecules), with liquid water (the formation of acid rain from sulphur dioxide), with vegetation (the direct effect of ozone), with mineral surfaces (soiling of buildings by particles) or with animals (respiratory damage by acidified aerosol). Pollution arising from human activities is called anthropogenic, while those having other natural 1 Terpenes are a class of natural products - a chemical compound or substance produced by a living organism i.e. found in nature. They consist of compounds with the formula (C 5H8)n and encompass >30,000 compounds. Terpenes are unsaturated hydrocarbons produced predominantly by plants, particularly conifers. origins (animals or plants) is said to be biogenic. Air pollution has been identified as a major problem in modern society, although in its conventional form of smoke and fumes, its origins date back to the Middle Ages, being closely associated with the Industrial revolution and the use of coal. Originally, air pollution was considered to include only substances from which environmental damage was anticipated because of their toxicity or their specific capacity to damage organisms or structures. However, the scope has been widened to include substances such as chlorofluorocarbons, ammonia or carbon dioxide that have more general environmental impacts. Table 1.1 provides the most recently updated list of local and transboundary air pollutants along with the details of the international and legislative directives that regulate them in the UK. Table 1.1 Local and transboundary air pollutants along with their regulatory international and UK legislative directives. Air pollutants Directive PM – PM10, PM2.5, NOx, O3, SO2, PAHs, Benzene, 1,3- Air Quality Strategy butadiene, CO, Pb SO2, NH3, NOx, NMVOC NECD (National Emissions Ceilings Directive) SO2, NH3, NOx, NMVOC, Heavy Metals, POPs CLRTAP (Convention on Long Range Transboundary Air Pollutants) 91 compounds including: CH4, CO, CO2 HFCs, N2O, E-PRTR (European Pollutant SF6, NH3, NMVOC, NOx, PFCs, SOx, CFCs, As, Cd, Cr, Release and Transfer Register) Cu, Hg, Ni, Pb, Zn, PM10, Benzene, HCl, HF, PAHs, which succeeds the EPER PCBs, PCDD, PCDF, Gamma HCH, PCP, HCB (European Pollutant Emission Register) SO2, NOx, CO, VOCs, metals, dust, asbestos, chlorine IPPC (Integrated Pollution and its compounds Prevention & Control) SOx, NOx, PM LCPD (Large Combustion Plants Directive) Dust (PM), HCl, HF, SO2, NOx, Heavy metals, Dioxins WID (Waste Incineration and Furans, CO Directive) VOC Solvent Emissions Directive VOC Paints Directive SO2 The Sulphur Contents of Liquid Fuels Directive VOC Petrol vapour recovery SO2, NOx, PM, Lead, Benzene, CO, Ozone, PAH, EU Air Quality Directives Cadmium, Arsenic, Nickel, Mercury Totally unpolluted air is probably impossible to obtain in a modern industrial society. Hippocrates, the ancient Greek physician, noticed the harmful effects of breathing polluted air over 2,000 years ago. By the thirteenth century, air pollution in London was so bad a commission was established to address the problem. However, at this time, air pollution was a local issue, being generated by hearths and furnaces. Today, problems caused by air pollution range from the local to the global scale, and occur on a variety of time-scales. Air pollution is not just unpleasant. In 1930, over 60 people died in the Meuse Valley, Belgium, due to extremely high levels of industrial air pollution. In 1948, in Donora, Pennsylvania (USA), 20 deaths and nearly 6,000 air pollution-related illnesses were recorded amongst a total population of just 14,000 as a consequence of industrial air pollution. In December 1952, several thousand people died as a result of a “killer fog” that settled over London. The terrorist attack on New York in 2001 had significant impacts on air quality, most visibly in the form of a huge dust cloud that spread rapidly after the Twin Towers of the World Trade Centre collapsed. Thousands of tonnes of debris resulting from the collapse of the Twin Towers contained more than 2,500 contaminants, including known carcinogens. Subsequent debilitating illnesses among rescue and recovery workers are said to be linked to exposure to these carcinogens. The Bush administration ordered the Environmental Protection Agency (EPA) to issue reassuring statements regarding air quality in the aftermath of the attacks, citing national security; however, the EPA did not determine that air quality had returned to pre-September 11 levels until June 2002. Air quality is currently a global “hot topic.” There are many reasons for this, including: The global response to Greta Thunberg’s School strikes; Widespread and increasing concern about the adverse impacts of climate change; Litigation by the environmental charity Client Earth against local and national governments across the EU to increase pressure to reduce air pollution and meet legal limits set to protect human health; The ruling in December 2020 by Southwark Coroner's Court in London that found air pollution "made a material contribution" to the death of 9-year-old Ella Adoo-Kissi- Debrah - possibly the first time ever that air pollution has been recognised as a cause of a person's death. The ruling in November 2022 by Rochdale Coroner’s Court that indoor pollution, in the form of mould spores caused the death of 2-year old Awaab Ishak. Measured reductions in air pollution during Covid-19 lockdowns as a consequence of reduced use of motor transportation and increased active transport (i.e. walking and cycling). India, and specifically Delhi’s extraordinary ongoing winter-time air pollution problem, caused primarily by a lack of water. The remarkable January 2022 wintertime wildfires in Colorado and the devastating wildfires in Los Angeles in early 2025. Astonishingly, such wildfires were foreseen by researchers from the University of California in Los Angeles in a paper published on 9 January 2025 (https://doi.org/10.1038/s43017-024-00624-z), just days before the fires took hold. London mayor Sadiq Khan’s unprecedented statement that 2022 London faces a crisis of "filthy air and gridlocked roads" unless car use is reduced. The peak air pollution episode in London in January 2023. When air pollution reached the top value of 10 on the government’s index. The failure of the so-called Climate and Nature Bill in January 2025. The government won a motion to end debate of the bill. The bill would have required the environment secretary to create and implement a strategy - with annual targets - to reduce its carbon dioxide emissions and reverse the degradation of nature. We are starting to properly understand the consequences of poor air quality, especially in urban areas. For example, the UK spends a staggering amount both directly on health care and indirectly as part of the welfare budget supporting those who cannot work due to poor health. These sums are widely regarded as unsustainable, and government therefore devotes a great deal of energy to encouraging citizens to take back responsibility for their own health through lifestyle choices such as healthy eating and exercise. There is growing evidence that where we live and our access to recreational space affects both our physical and mental well-being (Rydin et al. 2012; Shanahan et al.2015); this became particularly evident during Covid-19 lockdowns across the globe. For example, Southampton City Council opened “pop-up” temporary cycle lanes to support demand for active living during lockdowns (e.g. on Bassett Avenue between Winchester Road roundabout and Chilworth Road roundabout; on Hill Lane, between Bellemoor Road and Burgess Road). The argument is that if we can encourage people to get out, to be active and to enjoy their environment, we should be able to improve well-being and happiness (key government metrics) while also reducing the financial burden on the state (this is debateable). Given that a large and growing proportion of the world’s population lives in urban areas (e.g. 82% of the UK population), this can only be achieved if cities provide safe environments for exercise either as recreation or as part of the daily routine (e.g. commuting to work). In this context, “safe” includes both obvious physical factors (e.g. routes free from the dangers of crime and traffic) and invisible risks such as air pollution. According to the World Health Organisation (WHO), the annual cost of air pollution in the UK alone is £54 billion with 44,800 - 52,500 deaths per year attributable to particulates and NO2. Natural events can also cause significant air pollution. A “wildfire” is an uncontrolled fire in an area of combustible vegetation that occurs in the countryside area. Wildfires are known by other names, including brush fire, bush fire, desert fire, grass fire, forest fire, hill fire, peat fire, vegetation fire, and veldfire. Wildfires are 'quasi-natural' hazards because they can be caused by anthropogenic activities as well as being natural features (like volcanoes, earthquakes and tropical storms). The major natural causes of wildfire ignitions are lightning, volcanic eruption, sparks from rock falls, and spontaneous combustion. The most common anthropogenic sources of wildfires are deliberate lighting (to clear land for agriculture or just plain arson), discarded cigarettes, sparks from equipment, and power line arcs. Bush fires in Australia are a common occurrence because of the generally hot and dry climate. In the United States of America, there are typically between 60,000 and 80,000 wildfires each year. Wildfires emit considerable quantities of fine particulate matter and carbon dioxide. In our complex and rapidly changing modern society, we have to decide what level of pollution is acceptable to us. We have to decide what industrial compromise or cost we are prepared to accept to achieve an acceptable environmental quality, especially in our towns and cities where the majority of the world’s population is concentrated. In this module, we will focus on air quality, but clearly society has to consider all types of pollution simultaneously. This study unit provides an overview of the composition of the atmosphere and the main air pollutants. We start by examining the chemical composition of the atmosphere and reviewing the main air pollutants, before going on to classify those pollutants. Later sections are intended to give you a taster of the sorts of issues we shall be discussing later on in the module. Throughout the module we shall also be concerned with developing your ability to interpret, analyse and evaluate numerical air quality data. Here we shall be looking at the measurement of atmospheric pollution concentrations, the role of emissions inventories and the use of source emission data. After studying this unit you should be able to:  outline the chemical composition of the atmosphere, and explain the physical and chemical reasons why air is a mixture;  identify the major regulated and unregulated air pollutants;  use appropriate concentration units and averaging times, and inter-convert and interpret concentration units;  outline the major types and sources of air pollution;  explain the use of emissions inventories as an aid to pollutant monitoring;  use and interpret source emission data. 1.2 Composition of the atmosphere 1.2.1 Formation The atmosphere is the envelope of gases around the Earth. What we experience today as our atmosphere is a transient snapshot of its evolutionary history. Much of that history is scientific speculation rather than established fact. The planet Earth formed around 4,600 million years ago by the gravitational accretion of relatively small rocks and dust, called planetesimals, within the solar nebula. There was probably an initial primordial atmosphere consisting of nebula remnants, but this was lost to space since the molecular speeds exceeded the Earth’s escape velocity of 11.2 km s–1. A combination of impact energy and the radioactive decay of elements with short half-lives raised the temperature of the new body sufficiently to separate heavier elements such as iron, which moved to the centre. The same heating caused dissociation of hydrated and carbonate minerals with consequent outgassing of H2O and CO2. As the Earth cooled, most of the H2O condensed to form the oceans, and most of the CO2 dissolved and precipitated to form carbonate rocks. About one hundred times more gas has evolved into the atmosphere during its lifetime than remains in it today. The majority of the remaining gases was nitrogen. Some free oxygen formed (without photosynthesis) by the photolysis of water molecules. Recombination of these dissociated molecules was inhibited by the subsequent loss of the hydrogen atoms to space (hydrogen is the only abundant atom to have high enough mean speed to escape the gravitational attraction of the Earth). The effect of atomic mass makes a huge difference to the likelihood of molecules escaping from the Earth. The Maxwell distribution means that there is a most likely velocity that is relatively low, and a long tail of reducing probabilities of finding higher speeds. For example, a hydrogen atom at 600 K (typical temperature at the top of the atmosphere) has a 10–16 chance of exceeding escape speed, while the corresponding figure for an oxygen atom is only 10–84. This process will result in a steady attrition of lighter atoms. The first evidence of single-celled life, for which this tiny oxygen concentration was an essential prerequisite, appears in the fossil record from around 3,000 million years ago. Subsequently, the process of respiration led to a gradual increase in the atmospheric oxygen concentration. This in turn allowed the development of O3 that is thought to have been a necessary shield against solar UV. Subsequent evolution of the atmosphere has been dominated by the balance between production and consumption of both CO2 and O2. The composition of the atmosphere has fascinated natural philosophers since the earliest times – the Greeks regarded the air as one of the four elements (fire, earth, water and air). However, it was not until the late 17th century, when Robert Boyle described air as a “confused aggregate of effluviums”, that air was first regarded as a mixture. Even then, whilst oxygen and nitrogen were known to be the principal components of air, the question remained as to whether or not it was a mixture. Sir Humphrey Davy (1778-1829) thought that air was a compound, partly because if it were not a compound, then the heavier gas (oxygen) should sink below the lighter one (nitrogen) and, therefore, oxygen should be found in slightly higher concentrations at the very bottom of the atmosphere. The strength of the mixing process – caused by atmospheric turbulence – was not appreciated. The development of understanding that air is a mixture as opposed to a compound was based on the following reasons: the ratio of oxygen to nitrogen does vary, just slightly, from place to place; if air was a compound, the formula would be N15O4, which is very unlikely; the physical properties of air are identical to those of the appropriate mixture of nitrogen and oxygen (which make up about 99% of air); it is possible to separate the nitrogen and oxygen, which would not be possible if it was a compound; and there is no volume change or heat release on mixing oxygen and nitrogen, which suggests that a compound is not formed. Of course, we now know that air is a mixture of many gases, and not just oxygen and nitrogen. The typical composition of unpolluted, dry air at sea level is shown in Table 1.2. Note that the values given are for so-called “clean, dry air” – a hypothetical construct. So-called “Standard Dry Air” is the composition of gases that make up air at sea level. It is a standard scientific unit of measurement. Standard Dry Air is made up of nitrogen, oxygen, argon, carbon dioxide, neon, helium, krypton, hydrogen, and xenon. It does not include water vapour because the amount of vapour changes based on humidity and temperature. Because air masses are constantly moving, Standard Dry Air is not accurate everywhere at once. Nitrogen and oxygen make up about 99% of Earth’s air. Carbon dioxide, a gas that plants depend on, makes up approximately 0.04%. The values in Table 1.2 have not changed much over time except for methane, nitrous oxide and carbon dioxide, which have increased significantly since the Industrial Revolution, and are still rising. Thus the atmosphere of Earth derived primarily by thermal outgassing of volatile substances from virgin planetary material during and subsequent to the formation of the planet. The volatile substances included water present in the ocean, nitrogen in the atmosphere, and carbon dioxide, now largely residing in the sediments as carbonate deposits. Nitrogen gas (N2) is a primary outgassing product. It enters the biosphere – defined by Eduard Suess as "the place on Earth's surface where life dwells" - by bacterial nitrogen fixation, a process, which reduces N2 to amino compounds and incorporates it directly into the living cell. The biosphere eventually releases nitrogen to the atmosphere by anaerobic bacterial denitrification. Table 1.2. The composition of dry, unpolluted air at sea level in percent by volume (at a temperature of 15°C and a pressure of 101325 Pa). Gas Volume (%) Concentration (ppm or l dm-3) Nitrogen 78.08 780,800 Oxygen 20.95 209,500 Argon 0.93 9.300 Carbon dioxide 0.0417 424.6a Neon 0.0018 18.0 Helium 0.000524 5.2 Methane 0.0002 1.7 Krypton 0.00011 1.1 Nitrous oxide 0.00003 0.3 Hydrogen 0.00005 0.5 Ozone 0.000004 0.04 Xenon 0.0000087 a https://www.statista.com/statistics/. (Last accessed: 26/01/2025). In addition to a global rise, CO2 undergoes diurnal variations locally and annual variations globally due to assimilation and respiration by plants and the release from decaying biomass. Oxygen gas (O2) is not a planetary outgassing product but by-product of the assimilation of carbon dioxide (CO2) by phytoplankton (photosynthesizing microscopic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water) and green plants. Oxygen gas has evolved in over time in conjunction with the development of the biosphere. On a geological short time scale, the production and consumption of O2 is nearly balanced; a small fraction of organic material escapes re-oxidation by incorporation in marine sediments. The present amount of atmospheric oxygen is understood to represent an excess over that used up in the oxidation of organic carbon and other reduced chemical compounds. Carbon dioxide is readily absorbed by seawater. On a time scale of ~1,000 years, atmospheric CO2 is in equilibrium with that residing in the ocean. The majority of CO2 released by thermal outgassing has entered sediments in the form of limestone deposits. The exchange of CO2 with the biosphere via photosynthesis and re-oxidation of organic material occurs on a time scale of 10–100 years. The increase of CO2 in the atmosphere since the industrial revolution is caused by the combustion of fossil fuels that are taken from deposits of sedimentary organic carbon. Average annual atmospheric levels of CO₂ reached a record high of 424.61 parts per million (ppm) in 2024. Monthly atmospheric CO₂ concentrations peaked in June 2025, at 426.91 ppm. The rare gases in the atmosphere have resulted from planetary outgassing. The dominant isotope of argon, 40Ar, is a product of the radioactive decay of potassium-40. Trace gases include all those gaseous components in the atmosphere that – by virtue of their low concentrations – do not affect the bulk composition of air. This makes it convenient to quantify the local abundance of a trace gas by its molar mixing ratio (the chemical amount fraction). If reference is made to dry air, the influence of the variability of water vapour on the bulk composition of air is eliminated, and the molar mixing ratio becomes independent of changes in pressure and temperature. On the other hand, the presence of radicals, such as the hydroxyl radical (OH ), are customarily reported in terms of number concentration, although radicals undoubtedly also represent trace gases. Because the major components of air are chemically rather inert, atmospheric chemistry is for the most part driven by trace gases. The concentrations of atmospheric trace gases can be shown to adjust to a steady state (a situation in which all state variables are constant in spite of ongoing processes that strive to change them) between the sources and sinks and their global distributions. For trace gases that are long-lived, with residence times of 2 years or longer, the general circulation of the atmosphere guarantees a fairly uniform mixing ratio. For trace gases that are short-lived, the mixing ratio is determined by the local sources and sinks, and it may undergo substantial variations. In this case, the global distribution of sources and sinks as well as advection (a transport mechanism of a substance or conserved property due to the atmosphere's bulk motion) with the winds becomes important. 1.2.2 Major air pollutants Air pollutants could, in principle, be termed as any atmospheric constituents that exceed the concentrations listed in Table 1.2. However, strictly speaking, a pollutant is defined as a substance that is potentially harmful to the health or well-being of human, animal or plant life, or to ecological systems. Air pollutants may be classified in many ways but typically take either gaseous or particulate forms. We shall examine them both in detail later in the module, but for now it will useful to briefly identify the major ones. Unwanted chemicals or other materials can enter the atmosphere either from natural sources, such as volcanoes, dust storms and forest fires, or be from man made, known as anthropogenic, sources. The anthropogenic sources can be subdivided into stationary or point sources and area or mobile (linear) sources. Point sources include stacks, flues and chimneys. Area sources include groupings of usually small sources spread over an area, such as an industrial complex like a steel works or the combined emissions from domestic heating in a town. Mobile sources include cars, aeroplanes, ships and trains. Line sources are pollution that emanates from a linear direction - the most obvious linear sources are from roads and aircraft. Naturally occurring pollution includes particulates such as pollen and dust clouds. Volcanic eruptions can produce dust clouds of fine ash, as was recently seen when the Icelandic volcano Eyjafjallajökull erupted on 14 April 2010. Volcanic dust clouds can also contain potentially toxic material, such as crystalline silica. The ash cloud that formed from Eyjafjallajökull drifted across Europe during 2010, causing many countries to close their airspace and prevent aeroplanes from flying. The volcanic cloud posed a significant safety threat to aircraft - if planes flew through the ash cloud, particles in it could damage the engines and even cause them to fail completely. As most people spend about 90% of the time indoors, many common indoor air pollutants effect our health. These include CO and NO2 from faulty gas heaters and cookers, CO and benzene (C6H6) from cigarette smoke, and volatile organic compounds (VOCs) from synthetic furnishings, vinyl flooring and paints. There are also biological pollutants such as dust mites and mould. We can also divide air pollutants into regulated and unregulated, based on their treatment by environmental agencies in the United States, the European Union and major Asian countries. The major regulated pollutants are: sulphur dioxide (SO2); nitrogen oxides (NOx); carbon monoxide (CO); trace metals such as lead (Pb), cadmium (Cd) and platinum (Pt); organic compounds such as benzene and poly-aromatic hydrocarbons (PAH); and photochemical oxidants such as ozone (O3) and peroxyacetyl nitrates (PAN). Particulate matter includes a wide range of sizes (typically 0.01 m – >100 m) and may be composed of organic or inorganic materials (or mixtures). The types of particulate matter monitored include “total suspended particulates”, smoke and particles of a specific size, such as PM10 and PM2.5. Directive 2008/50/EC of the European Parliament and of the Council of 21st May 2008, on Ambient Air Quality and Cleaner Air for Europe, was adopted in June 2008. This Directive covers the following pollutants; sulphur dioxide, nitrogen oxides, particulate matter (as PM10 and PM2.5), lead, benzene, carbon monoxide and ozone. It revised and consolidated existing EU air quality legislation relating to these pollutants. The Fourth Daughter Directive (2004/107/EC) covers the four metallic elements cadmium, arsenic, nickel and mercury together with polycyclic aromatic hydrocarbons (PAH). The EEA website provides a useful source of up-to-date information and data on European air quality (https://www.eea.europa.eu/themes/air). The main examples of unregulated air pollutants are carbon dioxide (CO2) and nitrous oxide (N2O). 1.2.3 Water in the atmosphere The proportions given in Table 1.2 are for dry air, i.e. without water vapour molecules. The gases listed have long residence times in the atmosphere, are well mixed and their concentrations are broadly the same everywhere in the atmosphere. Water is very different, due to its unusual properties at normal Earth temperatures and pressures. It is the only material present in all three phases – solid (ice), liquid and gas (water vapour). There is continuous transfer between the three phases depending on the conditions. We take this situation very much for granted, but it is nevertheless remarkable. Certainly, if we found pools of liquid nitrogen or oxygen on the surface of the Earth, or drops of these materials were to fall out of the sky, it would get more attention. The proportion of water vapour in the atmosphere at any one place and time depends both on the local conditions and on the history of the air. First, the temperature of the air determines the maximum amount of water vapour that can be present. The water vapour pressure at this point is called the saturated vapour pressure (SVP), and varies roughly exponentially with temperature (Table 1.3). Table 1.3 Variation of saturated water vapour pressure with temperature Temperature (oC) Units -10 0 10 20 30 Pa 289 611 1223 2336 4275 mbar 3 6 12 23 43 Various mathematical expressions are used to describe the relationship; an adequate one for our purposes is:  19.65T  e s (T ) = 611 exp   273 + T  Pa where es(T ) is the saturated vapour pressure in Pa and T is the air temperature in degrees Celsius. Second, the ambient (meaning local actual) vapour pressure ea may be any value between zero and es. The ratio of actual to saturated vapour pressure is called the relative humidity hr, often expressed as a percentage. If water vapour is evaporated into dry air (for example, as the air blows over the sea surface or above a grassy plain), then the vapour pressure will increase towards es, but cannot exceed it. If air is cooled, for example by being lifted in the atmosphere, then a temperature will be reached at which the air is saturated due to its original water content. Any further cooling results in the ‘excess’ water being condensed out as cloud droplets. If the cooling occurs because the air is close to a cold ground surface, then dew results. The complexity of this sequence for any air mass is responsible for the variability of water vapour concentration in space and time. For comparison with the proportions given in Table 1.3 for the well-mixed gases, we can say that the highest vapour concentrations occur in the humid tropics, with temperatures of 30 °C and relative humidities of near 100%. The vapour pressure will then be 4300 Pa, corresponding to a mixing ratio of 4.3/101 = 4.3%. At the low end, an hr of 50% at a temperature of -20 °C would correspond to a mixing ratio of around 0.1%. The global average mixing ratio is around 1%, so the abundance of water vapour is similar to that of argon. 1.2.4 Measuring atmospheric composition The international system of units (Système International d’unités, SI) has now largely replaced all earlier systems of units used to describe physical quantities. SI is built upon seven base quantities each having its own dimension: length, mass, time, thermodynamic temperature, amount of substance (chemical amount), electric current, and luminous intensity. All other quantities are derived quantities that acquire dimensions derived. Although SI units are recommended for use in atmospheric chemistry, some non-SI units are still required e.g. time periods such as minute, hour, day and year, which can be expressed in terms of the second, but which defy decimalization. Where non-SI units are preferred, the appropriate conversion rule to SI units is typically indicated e.g. 1 atm = 101325 Pa. It is important to be aware of the way in which the composition of air is measured in atmospheric chemistry. There are two key aspects to this: the concentration of particular elements in the air; and the time over which the presence of an element is measured. Concentration units There are a number of different ways in which the concentration of gaseous pollutants may be expressed: the mass of gaseous pollutant per unit volume of air – usually measured in g m-3; the volume of gaseous pollutant per unit volume of air – usually measured in l l-1; the volume mixing ratio – usually measured in ppm (parts per million, 106), ppb (parts per billion, 109) or ppt (parts per trillion, 1012). For particulate pollutants, only the mass of pollutant per unit volume of air is applicable. The mixing ratio in atmospheric chemistry is defined as the ratio of the amount (mass, volume) of the substance of concern in a given volume to the amount (mass, volume) of all constituents of air in that volume. Here, air denotes gaseous substances, including water vapor, but not condensed phase water or particulate matter. Hence this unit of measurement expresses the concentration of a pollutant as a ratio of its volume, if segregated pure, to the volume of the polluted air in which it is contained, e.g. 1 ppm is equivalent to a cubic centimetre of gaseous pollutant in a cubic metre of air. The mixing ratio is frequently employed to quantify the abundance of a trace gas in air. The specific advantage of mixing ratio over concentration in this context is that the mixing ratio is unchanged by differences in pressure or temperature associated with altitude or with meteorological variability, whereas concentration depends on pressure and temperature in accordance with the equation of state. Since the mixing ratio refers to the total gas mixture, the presence of water causes the mixing ratio to vary somewhat with humidity. For this reason, it is preferable to refer to dry air when reporting mixing ratios of trace gases in the atmosphere whenever possible. The above definition of mixing ratio is identical to the fraction that the amount (mass, volume) contributes to the total amount (mass, volume) of the whole mixture. For gaseous species, chemical amount fraction and volume fraction are practically identical because air at atmospheric pressure is essentially an ideal gas. For gaseous pollutants, the inter-conversion between volume mixing ratios (ppm, ppb, etc) and mass per unit volume needs some explanation. As you can see from Table 1.1, the atmospheric volume occupied by gaseous air pollutants is tiny. Consequently, we can assume that air pollutants behave like a “perfect” or “ideal” gas. The molecules of an ideal gas occupy negligible volume and exert no forces upon one another. The volume mixing ratio is independent of temperature and pressure for an ideal gas (and, hence, for a gaseous air pollutant) because it is a ratio. However, volume is affected by temperature and pressure and so the mass per unit volume is dependent on temperature and pressure. The inter-conversion between the two must therefore incorporate these factors. The relationship between the volume mixing ratio and mass per unit volume is given by following equation:  molecular weight g m-3 = ppb x (Equation 1.1) molar volume (litres ) T 1013 where: molar volume = 22.4 x x 273 P in which: 22.4 = volume (in litres) occupied by one mole of gas at one atmosphere of pressure (1013 mb) and 273 K (0C) T = absolute temperature (K) P = atmospheric pressure (mb or Torr) Similarly, by cross multiplying, we can express the volume mixing ratio as: molar volume (litres) ppb = g m-3 x (Equation 1.2) molecular weight Example 1.1 To convert 100 ppb of NO2 at 293K and 1000 mb into g m-3: NO2 has a molecular weight (from the atomic weights of nitrogen, 14, and oxygen, 16) of 14 + 16 + 16 = 46. Using Equation 1.1, we get the following: 46 g m-3 = 100 x 293 1013 22.4 x x 273 1000 = 189 Therefore, 100 ppb of NO2 at 293 K and 1000 mb = 189 g m-3 For reference, some commonly used conversion factors are set out in Table 1.4. An atmospheric pressure of 1013 mb (one atmosphere) has been assumed. Table 1.4. Conversion factors at 1013 mb and different temperatures. Molecular Temperature Pollutant weight 273K 293K 298K Conversion factors (g m to ppb) -3 CO 28 0.800 0.859 0.873 NO2 46 0.487 0.523 0.532 O3 48 0.467 0.500 0.509 SO2 64 0.350 0.376 0.382 C6H6 78 0.287 0.308 0.313 Conversion factors (ppb to g m-3) CO 28 1.250 1.165 1.145 NO2 46 2.054 1.913 1.881 O3 48 2.141 2.000 1.965 SO2 64 2.857 2.704 2.617 C6H6 78 3.482 3.244 3.190 Averaging time The second key aspect of measuring the atmospheric pollution concentrations is the time over which the measurement is carried out. This is the “averaging time”. Thus, hourly, daily and weekly concentrations are often calculated and used when defining air quality standards. The averaging time selected for use depends upon the physico-chemical characteristics and health/environmental impacts of the pollutant under consideration. So, for example, a pollutant such as ozone, which can rise to a high concentration over a short period of time and can cause severe damage to crops, will often have a short averaging time. Seasonal averaging periods are also used. Typically, “winter” refers to the October – March period, whilst “summer” refers to April – September. 1.3 Classification of Air Pollutants The health and environmental consequences of air pollutants follow from three processes: the emission of pollutants from source; the transport of pollutants; and pollutant deposition. We shall consider the sources, transport and effects of specific pollutants later in the module. Here, we develop a classification of air pollutants based on general sources and effects, and introduce the way in which emissions are measured. 1.3.1 Types of air pollutants Our first classification is based on the way in which pollutants are formed in the atmosphere. Primary pollutants are those which are emitted directly into the atmosphere – for example, CO comes directly from the incomplete combustion of fossil fuels in motor vehicles and SO 2 is emitted from power stations and industrial plants. Secondary pollutants are formed in the air as a result of chemical reactions with other pollutants and atmospheric gases – for example, ozone is generated by photochemical reactions within the atmosphere. Note that pollutants do not necessarily fall into one or other of these categories – some can be both primary and secondary pollutants. For example, NO2 is emitted directly into the atmosphere from power stations and vehicle exhaust, and some is also formed from the oxidation of NO in the air. The distinction between the two types is important for understanding air pollution and devising appropriate control strategies. For primary pollutants, there is likely to be a proportional relationship between emissions and ambient concentrations. However, with a secondary pollutant, reducing emissions of its precursors may not necessarily lead to a proportional reduction in its ambient concentrations – indeed, in some circumstances, it may actually lead to an increase in concentrations. 1.3.2 Sources of air pollutants Definite sources of air pollutants can be identified and these emission sources may be classified as either: natural – including volcanic eruptions, sand storms, lightning and forest fires; or man-made or anthropogenic – the major source being the combustion of fossil fuel for energy, particularly in power stations and motor vehicles. There are, though, many non- combustion-related sources, including industrial processes, coal mining, domestic and industrial solvent use, natural gas leakage in the national distribution network, and landfill. Non-combustion sources are particularly important for volatile organic compounds and methane. Anthropogenic pollution sources may be further sub-divided according to their geographical distribution. There are three basic types: point sources – large, geographically-concentrated emitters whose emission rates are large enough to be significant by themselves even if no other sources are present, such as (coal fired) power stations, steel mills, oil refineries, pulp and paper mills, etc.; area sources – collections of small geographically dispersed emitters that are not significant individually, but are important collectively, such as residential and commercial areas, and also including agricultural emissions; line sources – a collection of relatively small sources that are distributed roughly uniformly along a line, such as a motorway or industries along a major river, a main road or railway line. The distinction between line and area sources is somewhat vague, with a busy city street, for example, being classified as either an area or a line source. 1.3.3 Source emission data In addition to expressing them as concentrations, pollution levels can be grouped according to their emission from the various different sources. Emission data may be used in two ways: to identify the main sources of individual pollutants; and to estimate levels of pollutants where such levels cannot easily be measured on their own – in which case mathematical models based on emission data are employed. The variety of air pollution sources makes estimating the emissions of specific atmospheric pollutants a demanding and time-consuming process. The basis of the process is the systematic compilation of detailed information on pollutant emissions in a given area in the form of an emissions inventory. Emissions inventories An air pollutant emissions inventory is a schedule of the sources of an air pollutant or pollutants within a particular geographical area. The inventory usually includes information on the amount of the pollutant released from major industrial sources, as well as average figures for the emissions from smaller sources and from transport throughout the area. By identifying the sources of air pollutants, an atmospheric emissions inventory can be used as an aid in interpreting air quality measurements. In an emissions inventory, data are collected for the three types of sources (line, area and point) within the selected geographical area. Clearly, it is impractical to measure every emission source in a large area. The majority of emissions are, therefore, estimated from other local information such as fuel consumption figures, vehicle kilometres travelled, or some other activity relating to pollutant emissions. Emission factors are then applied to the activity data in order to estimate the likely emissions. An emission factor is a number that represents the relationship between the mass of a given pollutant emitted from a particular source and the given amount of raw material processed. This may be expressed as: Activity rate x Emission factor = Emission rate Example 1.2 Particulate Elemental Carbon (PEC) is an important urban pollutant generated by diesel vehicles. In order to estimate the mass of PEC emitted from diesel vehicles in London in a given year (Q), the following equation may be used: Amount of fuel PEC emission factor consumed in Londonx = Amount of PEC emitted (% by mass) for Year Q 50 kT X 0.2 % = 1000 T of PEC emitted Emission Units Pollutant emissions are presented using a number of different mass and / or toxicity units, according to convenience, with specific reporting protocols including: NOx emissions are quoted in terms of NOx as NO2 SOx emissions are quoted in terms of SOx as SO2 PCDD and PCDF are quoted in terms of mass, but accounting for toxicity (the I-TEQ scale) Pollutant emissions are quoted as mass of the full pollutant unless otherwise stated, e.g. NH3 emissions are mass of NH3 and not mass of the N content of the NH3. UK and EU emissions inventories In the UK, the National Atmospheric Emissions Inventory (NAEI) collates emissions of over 30 major pollutants (http://naei.beis.gov.uk/data/emission-factors). They apply hundreds of different emission factors to fuel consumption and other national statistics to calculate totals, disaggregated breakdowns, spatial distributions and temporal trends of pollutants. Estimates are made of emissions from seven categories of stationary combustion source; mobile sources including road vehicles, off-road vehicles, aircraft and others such as trains and shipping; seven categories of industrial process; offshore oil and gas; construction; solvent use. The UK Department for Business, Energy & Industrial Strategy (BEIS) publishes an emission factor database (http://naei.beis.gov.uk/data/ef-all), so that, for example, a local authority that has compiled a list of processes and activities within its area that might generate emissions can make a first estimate of the emissions and decide whether a more detailed assessment is required. Urban inventories have also been compiled for selected major urban areas in the UK. These give contributions from line, area and point sources within 1 × 1 km squares, separated according to type of source. The UK emissions inventory estimates annual pollutant emissions from 1970 to the most current inventory year for the majority of pollutants. A number of pollutants are estimated from 1990 or 2000 to the most current inventory year due to the lack of adequate data prior to the later date. The scope of pollutants and years for which they are compiled varies according to data availability and inclusion of new pollutants in the inventory is usually driven by legislation. However, the UK government is pro-active in this area and the inventory includes emissions of pollutants which are not currently required by international or national reporting obligations, but which are of use to various areas of the scientific community. For example, reporting emissions of base cations allows the modelling community to better estimate the impacts of acidic gases. Pollutants that have to be reported to the Convention on Long-Range Transboundary Air Pollution (CLRTAP) include: Main pollutants (nitrogen oxides, sulphur dioxide, carbon monoxide, non-methane volatile organic compounds, ammonia) Particulate matter (PM10, PM2.5, Total Suspended Particulates) Priority heavy metals (lead, cadmium, mercury) Other heavy metals (copper, zinc, nickel, chromium, arsenic, selenium) Persistent organic pollutants (benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, indeno (1,2,3-cd)pyrene, polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDF), polychlorinated biphenyls, HCH, hexachlorobenzene) (N.B. PCDDs are a group of organic polyhalogenated compounds that are significant environmental pollutants. They are commonly but inaccurately referred to as dioxins for simplicity, because every PCDD molecule contains a dioxin skeletal structure as the central ring. PCDFs are a group of halogenated organic compounds that tend to co-occur with PCDDs.) Improvements to methodologies are logged continually, and are reviewed periodically. The UK emissions inventory is responsible for reporting the pollutants covered under the EU National Emissions Ceilings Directive (NECD) and the UNECE Convention on Long-Range Transboundary Air Pollution. The Gothenburg Protocol forms a part of the Convention on Long-range Transboundary Air Pollution (more detailed information on both of the Gothenburg protocol and the Convention may be found at the UNECE web site: https://unece.org/environmental-policy/air/international-cooperation-air-pollution); a brief history of the Gothenburg Protocol can be found in Box 1.1. The Gothenburg Protocol was revised in 2012 to set more stringent emission ceilings applicable from 2020 to 2029, and then further reduced ceilings applicable from 2030 onwards. It is likely to be revised again soon (see https://unece.org/environment/press/governments-europe-and-north-america-agree- revise-gothenburg-protocol-avoid-long). The revised NECD (2016/2284/EU) implemented these emissions ceilings for EU Member States. The ceilings due to be enforced from 2020 also include emissions reduction commitments for PM2.5. Current ceilings and ceilings due to be enforced from 2020 and 2030 from the NECD are implemented in UK legislation by the National Emission Ceilings Regulations 2018 (NECR). Directive 2001/81/EC of the European Parliament and the Council on National Emissions Ceilings for NOx, SO2, NMVOC and NH3 sets upper limits for each Member State for the total emissions in a given year. These pollutants are responsible for acidification, eutrophication and ground-level ozone pollution. The Member States are required to prepare and annually update national emissions inventories and emissions projections for specified years for these pollutants. Parallel to the development of the EU NECD, the EU Member States together with Central and Eastern European countries, the United States and Canada have negotiated the ‘multi- pollutant’ protocol under the Convention on Long-Range Transboundary Air Pollution. The emission ceilings of this protocol are equal or less ambitious than those in the NECD. Box 1.1 The CLRTAP and the Gothenburg Protocol (from http://www.airclim.org/acidnews/new-gothenburg-protocol-adopted). The Convention on Long-Range Transboundary Air Pollution (CLRTAP) dates back to 1979 and covers 51 parties in Europe and North America. Cooperation under the convention includes development of policies and strategies to cut emissions of air pollutants through protocols with emission control obligations, exchanges of information, consultation, research and monitoring. The original Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone was signed in 1999 and entered into force in 2005. It has been ratified by 24 European countries, as well as by the EU and the United States. Based on a thorough scientific assessment of health and environmental benefits of pollution control, the costs and emission reduction potential of different abatement options, and an analysis of various least- cost solutions to achieve agreed interim environmental targets, varying national requirements in terms of emission reductions were established. These are given as binding national emission ceilings for 2010 for four pollutants (SO2, NOx, VOCs and NH3). Countries whose emissions have a more severe environmental or health impact and/or whose emissions are relatively cheap to reduce should make the biggest emission cuts. In principle, an emissions inventory attempts to make estimates of all known emissions to air in as high a level of disaggregation as is possible. However, by following international guidelines on emissions reporting, there are a number of known sources, which are deliberately not included in the inventory: Natural sources are not included in the national totals (although estimates of some sources are made). The inventory is a primary emissions inventory (as per international guidelines). Consequently re-suspension of e.g. particulate material is not included in the national totals (although estimates for some re-suspension terms are made). Cruise emissions from civil and international aviation are not included in the national totals. Estimates of “International” emissions such as shipping are made, and reported as memo items (excluded from the UK national totals). GHG emissions associated with short-term changes to the carbon cycle are not included; whilst this is not of particular concern here, the principle is extended to other pollutants. The geographical scope of reporting needs to be defined. The UK has associated Overseas Territories (OTs), Crown Dependencies (CDs) and Sovereign Bases (SBs). The exact definition of the UK varies under different protocols within the CLRTAP. Emission estimates for the relevant locations and pollutants are made so that the UK emissions accurately reflect those specified in the individual protocols. The only CD, OT or SB which is included in emission estimates is Gibraltar. However, Gibraltar is only included in the definition of the UK for some of the protocols within the CLRTAP Convention. The UK does not yet make emission estimates from inland waterways. An inventory agency is responsible for compiling the emission inventories, including the following roles and responsibilities: Planning Co-ordination with relevant government departments to compile and deliver the emission inventories to meet international reporting requirements and standards; Review of current performance and assessment of required development action;  Scheduling of tasks and responsibilities of the range of inventory stakeholders to ensure timely and accurate delivery of emissions inventory outputs. Preparation Drafting of agreements with key data providers; Review of source data & identification of developments required to improve the inventory data quality. Management Documentation & archiving; Dissemination of information to inventory stakeholders, including data providers; Management of inventory QA/QC plans, programmes and activities; Archiving of historic datasets (and ensuring the security of historic electronic data), maintaining a library of reference material. The emission inventory database is backed up hourly. Inventory Compilation Data acquisition, processing and reporting; Delivery of the Informative Inventory Report (IIR) and associated datasets to time and quality. Other organisations are contracted to compile emission estimates from specific sources, including agricultural emissions of NH3 and emissions of NH3 from non-agricultural sources. Note that UK-Air is a terrific on-line air pollution resource (https://uk-air.defra.gov.uk/). Impacts of the Use of Emissions Inventories and Regulation The combination of scientific estimations of air pollution releases with regulatory regimes has sometimes resulted in significant environmental improvements. Within the EU, the National Emission Ceilings Directive was agreed in 2001. It sets emission ceilings to be achieved from 2010 onwards for each Member State for the same four pollutants as in the Gothenburg Protocol. The UK has met current international targets to reduce total emissions by 2010 of four air pollutants that cause harm to people’s health and to the natural environment. In the most recent ten-year period of emissions estimates, there has been mixed progress in reducing emissions of air pollutants: Emissions of sulphur dioxide and nitrogen oxides have continued to fall in line with the long-term trend with much of the reduction as a result of the decreasing dependence on coal for power generation, although the rate of change has lessened in recent years. Emissions of sulphur dioxide and nitrogen oxides from energy industries have decreased by 90% and 66%, respectively, between 2012 and 2022. Emissions of nitrogen oxides and NMVOCs from road transport decreased by 49% and 60% respectively between 2012 and 2022. This is largely as a result of tighter emissions standards being introduced for petrol and diesel cars. For particulate matter, decreases in emissions from many sources, particularly from road transport and energy industries, have contributed to a decrease in overall emissions between 2012 and 2022 (18% reduction in PM2.5 emissions and a 7% reduction in PM10 emissions). However, emissions from other sources have increased over this period. Emissions of both PM10 and PM2.5 from domestic combustion have increased by 19% between 2012 and 2022, which reflects the greater popularity of domestic solid fuel appliances like wood-burning stoves. Other notable sources of emissions that have grown over this period include the industrial combustion of biomass based-fuels for PM2.5 and construction for PM10. Total annual emissions of NMVOCs have decreased by 15% between 2012 and 2022, however the sources of these emissions are changing. Emissions from food and  beverages production have increased by 27%, whereas fugitive emissions from fuels (for example pipeline leaks and gas flaring from oil production) have decreased by 45%. Annual emissions of ammonia have remained stable between 2012 and 2022. Information Dissemination Data from the National Atmospheric Emissions Inventory (NAEI) is made available to national and international bodies in a number of different formats. The NAEI team hold seminars with representatives from industry, trade associations, UK Government and the devolved administrations. Data is made available and accessible to the public via the Internet. The NAEI website is updated annually, giving the most recent emissions data and other information such as: temporal trends, new pollutants and methodology changes. The NAEI web pages may be found at: https://naei.energysecurity.gov.uk/. The web pages give easy access to the detailed emissions data and a general overview. Information resources available on the NAEI web pages include: Data Warehouse: - Emissions data is made available in numerous formats through a database. This allows extraction of overview summary tables, or highly detailed emissions data. Emissions Maps: - Emissions of pollutants are given in the form of UK maps. These maps give emissions of various pollutants on a 1 x 1 km resolution. Reports: - The most recent reports compiled by the inventory team on related subjects are made available in electronic format. Methodology: - An overview of the methods used for the compilation of the NAEI is on the website. In addition, the NAEI website provides links to webpages that explain technical terms, provide airborne pollutant concentration data and to sites that outline the scientific interest in specific pollutants and emission sources. In particular there are links to the various pages containing comprehensive measurement data on ambient concentrations of various pollutants. Further information on air quality in the UK and emissions of air pollutants is available from: UK-AIR– provides much of the air quality information in the UK, including: near real-time data from the UK national monitoring networks and a database of measurements from the networks A five-day air quality forecast as measured against the Daily Air Quality Index, and associated health advice. A reports library for air quality science and research, including work by the UK Air Quality Expert Group. Maps and summary statistics of Air Quality Management Areas designated by local authorities. NAEI website – provides a database of national emissions estimates for air pollutants and greenhouse gases, including a map of emission sources in the UK as well as emission factors and relevant reports. UK Pollutant Release and Transfer Register (PRTR) – a UK inventory for pollution from industrial sources that is released to air, water or soil. There is also a Europe-wide version known as E-PRTR run by the European Environment Agency that includes UK data. Department for Environment, Food and Rural Affairs (Defra) – a guide to air quality policy in England including the Clean Air Strategy 2019, updated in 2023. Scottish Government – a guide to air quality policy and monitoring in Scotland. Welsh Government – a guide to air quality policy and monitoring in Wales. Department for Agriculture, Environment and Rural Affairs – a guide to air quality policy and monitoring in Northern Ireland.  Public Health England – guidance on the effects of poor air quality on human health, and statistics on the mortality burden of PM2.5 by local authority. European Environment Agency – an agency of the European Union that provides sound, independent information on the environment. Local authorities also monitor air quality and produce annual status reports on local air quality. These reports are often published by the local authority online or are available by request. You can email [email protected] if you have any questions or comments about UK air quality and emissions information. The Annual Cycle of Inventory Compilation The NAEI is compiled on an annual cycle that encompasses: data collection, compilation, reporting, review and improvement. Each year the latest set of data are added to the inventory and the full time series is updated to take account of improved data and any advances in the methodology used to estimate the emissions. Updating the full time series, making re-calculations where necessary, is an important process as it ensures that: the full NAEI dataset is based on the latest available data, using the most recent research, methods and estimation models available in the UK; the inventory estimates for a given source are calculated using a consistent approach across the full time-series and the full scope of pollutants; all of the NAEI data are subject to an annual review, and findings of all internal & external reviews and audits are integrated into the latest dataset. The compilation of the UK inventory requires a systematic approach to the collation of quite disparate statistical and source emission measurement information, and the subsequent calculation of comprehensive, coherent and comparable air emissions data to a range of users. The compilation method can be summarised as follows: 1. Data Collection- source data are requested, collected and logged, from a wide variety of data providers. 2. Raw Data Processing- the received data is checked, and formatted for use. 3. Spreadsheet Compilation- formatted input data is added to spreadsheets to generate all required emission factors and activity data in the required format. 4. Database Population- emission factors and activity data are uploaded from the spreadsheets to the central emissions inventory database. 5. Reporting Emissions Datasets- data is extracted from the database and formatted to generate a variety of datasets used for national or international reporting requirements. The five-stage summary of the inventory cycle provides a simplistic overview. In practice, there are considerably more tasks and the cycle is more complex. For example, some other tasks within the programme would be associated with: Quality assurance and quality control (QA/QC) tasks and systems operate throughout the entire inventory programme; Management of the work programme, overseeing stakeholder engagement and inventory delivery as well as organising staff; Other Government support activities, which are conducted by the team. The major inventory for Europe is organised by the European Environment Agency under the project name EMEP/EEA air pollutant emission inventory guidebook (formerly called the EMEP CORINAIR emission inventory guidebook; CORINAIR = CORe Inventory of AIR emissions). This is a project performed since 1995 by the European Topic Centre on Air Emissions under contract to the European Environment Agency. The aim is to collect, maintain, manage and publish information on emissions into the air, by means of a European air emission inventory and database system. 1.4 Air Pollution and Human Health Clean air is a basic requirement of human well being. Air pollution poses a significant health threat to everyone, everywhere in the world. The range of health effects are broad, but are predominantly to the respiratory and cardiovascular systems. All the population is affected, but differences in health and age may make some people more susceptible. The risk has been shown to increase with exposure and even relatively low concentrations of air pollutants have been related to a range of adverse health effects. The low end of the range of concentrations at which adverse health effects have been demonstrated is not much above the background concentration. Air pollution can cause both immediate, known as acute, symptoms and long term, known as chronic, effects (see Figure 1.1). Acute symptoms include eye, nose and throat irritation, aching lungs, bronchitis and pneumonia, wheezing, coughing, nausea and headaches. Chronic effects include heart disease, chronic obstructive pulmonary disease, genotoxic effects such as leukaemias, lymphomas and lung cancer and airway sensitivity disorders such as asthma. According to a WHO assessment, more than two million premature deaths each year can be attributed to the effects of air pollution (WHO, 2008). By reducing air pollution levels, the global burden of these diseases, as well as reproductive and neurodevelopmental disorders, can be reduced. Table 1.5 shows the health effects of some of the common air pollutants. Figure 1.1. Summary of health effects of pollution (sourced from: www.commons.wikimedia.org (last accessed September 2010). Table 1.5. Air Pollutants and Health Source: European Commission: Clean air for Europe’s cities, 1997 (European Commission, 1999). Pollutant Main source Potential health effects Benzene Motor vehicles Causes cancer Chemical industry Affects the central nervous system Heavy Metals Industrial Processes Cause cancer (e.g. Arsenic, Energy Production Give digestive problems cadmium, lead, mercury and Motor vehicles Damages lung tissues nickel) Nitrogen Motor vehicles Causes respiratory problems Dioxide Other fuel combustion processes Damages lung tissue Ozone Transformation of nitrogen oxides and Produces respiratory problems volatile organic compounds produced Reduces lung function by traffic in the presence of sunlight Worsens asthma Irritates eyes and nose Reduces resistance to infections Particulates Fuel burning — e.g. diesel and wood Cause cancer Industry Produce cardiac problems Agriculture — e.g. ploughing, burning- Give rise to respiratory diseases off for fields Increase the risk of infant Secondary chemical reactions mortality Sulphur Fuel combustion Causes respiratory problems Dioxide Worldwide, an estimated one billion people in urban areas are continuously exposed to health hazards from air pollution. Most of the detrimental human health effects associated with AQ emissions are related to respiratory and cardiovascular disease, whilst some are also carcinogenic. Road traffic is often the dominant anthropogenic source of AQ emissions in urban areas, and poor local air quality in the vicinity of busy roads is of particular concern, especially as emissions occur in close proximity to people. It has been suggested that road traffic is likely to remain a major contributor to poor urban air quality over the coming decades. Fine particulate matter and ground-level ozone are the main threats to human health from air pollution in Europe. Fine particulate matter includes dust and soot that are suspended in, and move with, the air. Particle pollution can cause eye, nose and throat irritation and can also be carried deep into the lungs where they can cause inflammation and a worsening of heart and lung diseases. In 2009, the EU's Clean Air for Europe (CAFE) programme estimated a total of 348,000 premature deaths per year in Europe are due to exposure to fine particles (European Environment Agency, 2009). More up-to-date information from the World Health Organisation (WHO) suggests that the annual cost of air pollution in the UK alone is £54 billion with 44,800 - 52,500 deaths per year attributable to particulates and NO2. The health and social care costs of air pollution in England could reach £5.3 billion by 2035 unless action is taken, according to Public Health England (PHE). In 2017, the costs were £42.88 million. Local authorities will be able to use the tool to inform their policies to improve air quality (see: https://www.gov.uk/government/publications/air-pollution-a-tool-to-estimate- healthcare-costs). Ozone occurs in two layers of the atmosphere. When ozone forms in the Stratosphere at a height of 6 to 30 miles above the surface of the Earth, it protects life from the sun’s harmful ultraviolet (UV) rays. However, when it is in the Troposphere, which generally extends to about 6 miles up, it is a very harmful air pollutant. It is a main ingredient of urban smog. Ozone is formed in the atmosphere by photochemical reactions in the presence of sunlight and precursor pollutants, such as the oxides of nitrogen (NOx) and volatile organic compounds (VOCs). Breathing ozone can trigger a variety of health problems including chest pain, coughing and wheezing, eye, nose and throat irritation and congestion. It can worsen bronchitis, emphysema and asthma. It can also reduce lung function and inflame the linings of the lungs. Repeated exposure may cause permanent lung tissue scarring. Difficulty breathing is also experienced by healthy people when exposed to ozone pollution. Because ozone forms in hot weather, anyone who spends time outdoors in the summer may be affected, particularly children, outdoor workers and people exercising. The ozone in the Stratosphere is depleted by reactions with man-made chemicals referred to as ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. A reduction in the stratospheric ozone layer can cause increased amounts of UV radiation to reach the Earth. This can lead to more cases of skin cancer, cataracts and impaired immune systems. 1.4.1 Sick Building Syndrome and Building related Illness If occupants of a building experience various ailments and illnesses characterised by headaches, respiratory problems and skin irritations, although no specific illness or cause can be identified, the building is described as having 'Sick Building Syndrome'. This is thought to be caused by indoor pollutants, micro-organisms or inadequate ventilation. The 'syndrome' tends to be associated more with office blocks than factories and is a temporary phenomenon that is relieved when the affected person is no longer inside the building. There is a particularly high incidence in certain types of buildings, especially offices which are sealed and mechanically ventilated or air-conditioned (Health and Safety Executive, 2004). Building Related Illness describes symptoms of a diagnosable disease that can be linked to air pollution, such as Legionnaires disease. Possible causes are inadequate building ventilation, chemical contaminants and biological contaminants. 1.5 Air Pollution and the Environment The effect of air pollution on plants can be seen in a variety of ways - from visible markings on the foliage to reduced growth and yield or even to premature death of the plant. The level of injury depends on the concentration of the particular pollutant, and other factors, such as the length of exposure, the plant species and its stage of development and the preconditioning of the plant, which make it either susceptible or resistant to injury. Table 1.6 shows the major effects of various pollutants on plants. Some plants are more tolerant to air pollution than others. The London Plane tree, for example, sheds its bark and therefore stops air pollution reaching the inner trunk of the tree. However, the short, stiff hairs shed by the young leaves and the dispersing seeds of the London Plane are an irritant and can exacerbate breathing difficulties for people with asthma. Certain pollutants, both from natural and anthropogenic sources, accumulate in the atmosphere and are known as greenhouse gases. These include water vapour, carbon dioxide, atmospheric methane, nitrous oxide, ozone and chlorofluocarbons. Every day, sunlight strikes the Earth’s surface and warms the Earth. Some of this heat is then radiated back out towards space as infrared radiation. Greenhouse gases absorb some of this infrared radiation and traps it in the atmosphere, causing the Earth to heat up. If it were not for naturally occurring greenhouse gases, the Earth would be a lot colder than it is now. If there are sufficient concentrations of greenhouse gases in the atmosphere, they will cause the Earth’s temperature to rise. This is called Global Warming. The concentrations of these gases have increased dramatically since the industrial revolution. Estimates suggest that greenhouse gases may cause a gradual increase in the global surface temperature by 1.5 to 4 ˚C by the middle of the 21st Century, although the amount and timing of any temperature increases are speculative. Table 1.6. Summary of the major sources, impacts and scale of effects of the major air pollutants on plants (adapted from Emberson, 2003). Pollutant Major Sources Major Impacts Major Scale of Effects Sulphur dioxide Power generation; Visible folia injury; altered Local (SO2) industry; commercial and plant growth; elimination of domestic heating lichens and bryophytes; forest decline Nitrogen Oxides Power generation; Altered plant growth; Local (NOx) transport enhanced sensitivity to secondary stresses; eutrophication Ozone (O3) Secondary pollutant Visible folia injury; reduced Regional formed from NOx and growth; forest decline hydrocarbons Suspended Power generation; Altered plant growth; Local Particulate transport; industry; enhanced sensitivity to Matter (SPM) domestic heating secondary stresses Fluorides Manufacturing and Reduced plant growth; Local smelting industries fluorosis in grazing animals Certain types of air pollution, such as sulphur dioxide and nitrogen oxides, react with water, oxygen and other components in the air. The resulting precipitation is commonly called acid rain. It can fall as rain, snow, fog, and also as particles of dry material that settle to Earth. The precipitation is a mild solution of sulphuric and nitric acid. The wind can spread the acidic solution hundreds of miles, for example much of the acid rain that falls in Scandinavia is caused by air pollution generated in the UK. Acid rain enters water systems and sinks into the soil. It makes lakes and streams acidic and causes them to absorb aluminium. This combination then makes waters toxic to crayfish, clams, fish, and other aquatic animals. Acid rain robs the soil of essential nutrients and releases aluminium, which makes it hard for trees to take up water. Leaves and needles are also harmed by acids and it can also cause damage to buildings and structures. The only way to control acid rain is by reducing the release of the pollutants that cause it. Greenpeace’s view on the impacts of the bushfires crisis in Australia can be found here: https://www.greenpeace.org.uk/news/australia-fires-climate-change-horror-facts/. 1.6 Air Pollution and Animals Air pollution can directly and indirectly affect animals. Direct methods include breathing in gases or small particles, eating particles in food, water or from grooming themselves, or absorbing gases through the skin. Earthworms and other soft-bodied invertebrates, or animals with thin, moist skin, are the ones mainly affected by absorbing pollution. Particulates can be especially dangerous when they contain certain metals (e.g. heavy metals), as they can build up to high concentrations in the body tissues of animals. Indirect effects of air pollution include acid rain and Global Warming. Acid rain changes the acidity of the water that animals live in and drink from and can decrease the amount of trees that provide shelter, which both create serious problems for wildlife. Global Warming may, for example, destroy habitats, cause birds to lay their eggs earlier than usual and force mammals to break their hibernation sooner. It is estimated that almost half a billion animals have been killed by the 2020 Australian bushfires: https://www.bbc.co.uk/news/50986293. 1.7 Infographics Infographics (information graphics) have been identified as a useful approach to the successful communication of ‘Big Data’. Infographic use can make significant amounts of data understandable, even where lingual and cultural barriers exist. Infographics have been acknowledged as a powerful tool to increase public engagement with scientific research. Infographic studies have identified colour, visual complexity and size as significant design features, whilst data visualisation studies have noted the importance of number, scale and graphical embellishment (Table 1.7). Table 1.7. Components and features which may be useful for infographic design (table credit: Joshua Jones, Masters student). Component Feature Findings Colour Single preferences Overall British adults: Individually, cool colours (green, cyan, blue) preferred to warm colours (red, orange, yellow). Blue most popular, yellow to yellow-green is least popular individually. Age studies have focussed on infant versus adult differences in colour preference rather than within the adult population. Infants have been found to have a stronger looking preference for dark yellow, and weaker for blue. Gender. British adults: Females prefer reds and purples, whilst males prefer blue-green. Culture. British preferences are different to non-industrialised Himba adults in rural Namibia. Health. Red-green dichromats: yellow is most preffered rather than the least, weaker preference for blue. Combination Colour combinations of text on background depend on infographic format. Printed: Black/yellow the best preferences text/background combination on the Le Courier legibility table. Numbers and General numeracy Gender: Among the general population, gender differences do not exist in mathematical ability. Sociocultural factors scale rather than innate biological differences are the explanation where males outperform females. Age: Older adults (65+) make more errors when interpreting numerical information from figures than those aged 18- 64. A comparison of 18-24 with (61-89) also indicated significantly lower numeracy. Visualisation type Unique visualization types (pictoral, grid/matrix, trees and networks, and diagrams) were significantly more memorable than common graphs (circles, area, points, bars, and lines). Bar graph most popular overall when asked to select graph which enhanced their understanding. Simple line graph preferred for quick assimilation of data. Bar graphs chosen more for detail than quick trends. Multiple axes Clear visual breaks should be used between datasets represented on multiple axes. Annotations Can improve understanding of numbers and scale on graphs. But do have negative effects on memorability. Graphical Embellishment with Charts embellished with imagery were not more difficult to interpret than plain graphs. Long-term recall of the embellishments imagery embellished graph was higher than the plain graphs. Visual Text versus diagrams Overall: Text-heavy infographics are lowest rated in terms of visual complexity. complexity Gender: Females less impressed by visually complex infographics. Males prefer more images on the infographic. Age: Older people did not like visually complex infographics. Education: Highly educated people less attracted to visually complex infographics. High visual density infographics are more memorable. Visualisations with pictograms have higher memorability than text. Size Large versus small 70% of subjects read the large infographic before the headline or text of newspaper articles. Colour has higher memorability than black-white images, and a greater number of colours can increase the memorability of visualisations. Males and highly educated people have been reported to be less impressed by colour. In terms of specific colour preferences, research has focussed on single colours with notable differences reported according to gender, age, culture, and health (Table 1.7). Colour combinations have comparatively received less attention. The optimum two colour combinations in terms of text/background contrast have been investigated, but some colour combination contrasts are yet to be researched. Numbers and scales that are displayed on infographics are often complex or new to the reader. Numeracy varies according to a number of factors, which has implications for infographic design. It may sometimes be better to visualise data without displaying numbers and scales. Infographics with increased visual complexity or density are generally preferred as they have increase the memorability of visualisations. Preferences for visual complexity vary according to age, gender and education. Graphical embellishments have been identified as an opportunity to increase the memorability of graphs; however, user preferences regarding graphical embellishment are yet to be investigated. When designing an infographic, it is recommended that the target audience is identified. Age and gender have different infographic preferences. However, the influence of scientific knowledge on infographic preference and understanding has been comparatively ignored. This is an oversight, assuming that professional users of scientific information more comfortable with complex scientific information than the layperson. Hence, although communicating the implications of air pollution scenarios is challenging, infographics have been identified as a method to communicate large amounts of data. 1.8 Chapter Summary After careful study of this session, you will understand the chemical composition of the atmosphere and be able to identify key air pollutants. In addition, you will understand the meaning of terms frequently used in air pollution science and you will have started to use and interpret air pollution data. You can use the following self-study exercises to test your knowledge and monitor your progress to date (the answers will be discussed/provided in the next tutorial). https://sotonac-my.sharepoint.com/personal/idw_soton_ac_uk/Documents/Stuff/Lectures/AQEP/Module Notes/Week1/Current/FirstPrinciples-25.docx Self-Study Exercices 1.1 Identify the four gases that compose more than 99.9% of the volume of the atmosphere. 1.2 Identify the major regulated air pollutants. 1.3 What are the units associated with: (a) gaseous air pollutants (b) particulate air pollutants? 1.4 Convert: (a) 50 ppb of ozone (O3) at 298 K and 1005 mb to g m-3 (b) 12 ppb of toluene (C7H8) at 283 K and 1010 mb to g m-3 (c) 5 ppm of carbon monoxide (CO) at 291 K and 1018 mb to mg m-3 1.5 Convert: (a) 51 g m-3 of sulphur dioxide (SO2) at 293 K and 1011 mb to ppb (b) 175 g m-3 of nitrogen dioxide (NO2) at 279 K and 1001 mb to ppb (c) 350 mg m-3 of carbon dioxide (CO2) at 300 K and 1020 mb to ppm 1.6 Define the terms: (a) Secondary pollutant (b) Anthropogenic pollutant (c) Area source (d) Emissions inventory (d) Volume mixing ratio (e) Emissions map 1.7 Classify the following pollutant sources: (a) a motorway (b) a coal mine (c) a large supermarket complex (d) a steam engine (e) a nuclear power station (f) a hospital incinerator 1.8 Give examples of how air pollution can damage human health. Include chronic and acute health effects. Give some examples of how air pollution in Australia has recently affected firefighters and tennis players. 1.9 Create a list of indoor air pollutants and their sources. E-mail your tables (with sources fully referenced) to the tutor ([email protected]). 1.10 Create a table that shows the sources, effects, typical concentrations social and health costs of air pollutants for a country of your choice. E-mail your tables (with sources fully referenced) to the tutor ([email protected]). 1.11 Imagine you are a policy maker for the day. Using available data, draw up a five- point plan to reduce air pollutant emissions in the UK in the most cost-effective fashion. 1.12 It could be argued that spatial and temporal variation in air quality in cities renders mean values inadequate for assessing the risks of air pollution on health during physical activity. What are your views on this debate? Professor Ian Williams https://sotonac-my.sharepoint.com/personal/idw_soton_ac_uk/Documents/Stuff/Lectures/AQEP/Module Notes/Week1/Current/FirstPrinciples-25.docx