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• Air, the Earth's chemical envelope, sustains life with at least 3000 identified chemicals.
• Air pollution is defined as atmosphere contaminants causing harm to humans, the environment, and air quality.
• An air pollutant is any chemical species exceeding natural air constituents' concentrations or characteristics.
• A pollutant is a substance potentially harmful to the health/well-being of humans, animals, plants, and/or ecological systems.
• Pollution includes human-introduced substances or energy causing hazards to health, resources, ecosystems, structures, amenity, or environmental use.
• Volcanic sulphur dioxide and natural methane are not pollution, but sulphur dioxide from coal burning and methane from rice crops are.
• Radon is not pollution as it's not from human activity.
• Human-caused pollution is anthropogenic, while natural pollution is biogenic.
• Air pollution is linked to the Industrial Revolution and coal use, and now includes substances like chlorofluorocarbons, ammonia, and carbon dioxide.

Local and Transboundary Air Pollutants

• PM, NOx, O3, SO2, PAHs, and benzene are air pollutants covered by the Air Quality Strategy.
• SO2, NH3, NOx, NMVOC are air pollutants covered by by the National Emissions Ceilings Directive.
• CLRTAP regulates SO2, NH3, NOx, NMVOC, heavy metals, and POPs.
• E-PRTR covers 91 compounds including: CH4, CO, CO2 HFCs, N2O, SF6, NH3, NMVOC, NOx, PFCs, SOx, and CFCs.
• IPPC regulates SO2, NOx, CO, VOCs, metals, dust, asbestos and chlorine.

Historical Air Pollution Events

• Hippocrates noted air pollution's harmful effects over 2,000 years ago.
• London established a commission to address air problems by the thirteenth-century.
• In 1930 in Belgium, industrial air pollution killed 60.
• In 1948, Donora, Pennsylvania had 20 deaths and 6,000 pollution-related illnesses due to industrial air pollution.
• A "killer fog" in London in December 1952 resulted in several thousand deaths.
• The 2001 New York terrorist attack significantly impacted air quality with a dust cloud containing over 2,500 contaminants, including carcinogens.
• EPA ordered to issue reassuring statements post-attack but air quality did not return to pre-September 11 levels until June 2002.

Current Air Quality Concerns

• Global awareness increased because of Greta Thunberg's School strikes.
• There's growing concern about climate change impacts.
• There's litigation against governments in the EU to reduce air pollution.
• Air pollution deemed a material contribution to Ella Adoo-Kissi-Debrah's death by a Southwark Coroner's Court in December 2020.
• Indoor mould spores caused Awaab Ishak's death per Rochdale Coroner's Court in November 2022.
• Motor transport reductions during COVID-19 lockdowns improved air quality.
• India, specifically Delhi faces winter air pollution due to lack of water.
• January 2022 saw Colorado wintertime wildfires and early 2025 saw Los Angeles wildfires.
• Sadiq Khan stated London faces a crisis of "filthy air and gridlocked roads" sans car use reduction in 2022.
• The a peak air pollution episode occurred in London in January 2023.
• The Climate and Nature Bill failed in January 2025.

Air Quality and Societal Impacts

• The UK faces significant health and welfare costs due to poor air quality.
• Government promotes lifestyle changes for better health.
• Access to recreational space affects physical and mental well-being.
• Southampton City Council added temporary cycle lanes during COVID-19 lockdowns.
• Initiatives aim to improve well-being and reduce state financial burden.
• Urban areas need safe exercise environments (recreational and commuting).
• "Safe" environments include freedom from crime, traffic, and air pollution.
• The WHO estimates the UK's annual cost of £54 billion with 44,800 to 52,500 deaths from air pollution (particulates and NO2).

Natural Air Pollution Sources

• Wildfires (brush, bush, desert, grass, forest, hill, peat, vegetation, and veld fires) are uncontrolled fires in countryside areas.
• They are quasi-natural hazards, also caused by human activities.
• Natural wildfire causes include lightning, volcanic eruption, rock fall sparks, and spontaneous combustion.
• Anthropogenic wildfire causes include deliberate lighting, discarded cigarettes, equipment sparks, and power line arcs.
• Bush fires are common in Australia’s hot, dry climate.
• The USA typically sees 60,000 to 80,000 wildfires annually.
• Wildfires emit fine particulate matter and carbon dioxide.

Air Quality Decisions

• Modern society has to decide on acceptable pollution levels.
• We must decide on acceptable compromises/costs for environmental quality in concentrated areas, especially in towns and cities.
• This module focuses on air quality amid all pollution types.

Module Overview

• This study unit examines the atmosphere's composition and main air pollutants.
• Later sections will provide a taster of issues to be discussed.
• Measurement, analysis, and evaluation of numerical air quality data are important.

Learning Outcomes

• Outline atmosphere chemical composition and explain air as a mixture.
• Identify major regulated and unregulated air pollutants.
• Use, convert, and interpret concentration units and averaging times.
• Outline major air pollution types and sources.
• Explain emissions inventories for pollutant monitoring.
• Use and interpret source emission data.

Atmosphere Composition

• Today's atmosphere is a transient snapshot of its history, mainly scientific speculation.
• Earth formed 4,600 million years ago from planetesimal gravitational accretion within the solar nebula.
• An initial atmosphere was lost to space; molecular speeds exceeded Earth's escape velocity (11.2 km/s).
• Impact energy and radioactive decay separated heavier elements (e.g., iron to the center).
• Heating caused dissociation of hydrated/carbonate minerals, releasing H2O and CO2.
• Cooling Earth condensed H2O into oceans; CO2 dissolved and formed carbonate rocks.
• The majority of remaining gases was nitrogen.
• Free oxygen formed (without photosynthesis) by water photolysis.
• Hydrogen loss to space inhibited re-association of molecules (hydrogen has the highest mean speed).

Effect of Atomic Mass on Atmospheric Composition

• Atomic mass greatly reduces likelihood of escape.
• Maxwell distribution means there is a relatively low most likely velocity, and a long tail of reducing probabilities of finding higher speeds.
• Hydrogen atoms at 600 K have a 10^-16 chance of exceeding escape speed; oxygen atoms have only 10^-84.
• This led to a steady loss of lighter atoms.

Early Life and Atmospheric Oxygen

• First evidence of single-celled life (requiring tiny oxygen concentration) is in fossil records from 3,000 million years ago.
• Respiration gradually increased atmospheric oxygen.
• Ozone (O3) became a necessary shield against solar UV radiation.
• Atmosphere evolution involved a balance between production and consumption of CO2 and O2.

Early Atmospheric Theories

• The Greeks viewed air as one of four elements (fire, earth, water, air).
• Robert Boyle regarded air as a "confused aggregate of effluviums" in the late 17th century.
• Oxygen and nitrogen were known as principal air components.
• Sir Humphrey Davy thought air was a compound; heavier oxygen should sink below lighter nitrogen.
• Atmospheric turbulence mixing strength wasn't appreciated.

Understanding Air as a Mixture

• The ratio of oxygen to nitrogen varies slightly by location.
• If air were a compound, the formula would be N1.5O4, which is very unlikely.
• Physical air properties match appropriate nitrogen and oxygen mixtures (99% of air).
• Nitrogen and oxygen can be separated—impossible if it was a compound.
• Volume change/heat release doesn't occur when mixing oxygen and nitrogen.

Modern Understanding of Air

• Air is a gaseous mixture.

• Sea level unpolluted, dry air composition is shown (values are for "clean, dry air," a construct).

• "Standard Dry Air" is sea level gas composition, a scientific measurement made up of nitrogen, oxygen, argon, carbon dioxide, neon, helium, krypton, hydrogen, and xenon.

• Standard Dry Air doesn't include water vapor because the amount varies by humidity and temperature.

• Air masses are moving constantly means Standard Dry Air isn't accurate everywhere.

• Nitrogen and oxygen make up ~99% of Earth's air.

• Carbon dioxide, which plants require, makes up roughly 0.04%.

• Data haven't shifted much except for rising methane, nitrous oxide, and carbon dioxide since the Industrial Revolution.

Earth's Atmosphere Origin

• It's primarily from thermal outgassing of virgin matter during/after planetary formation.
• The volatile components included water (in the ocean), nitrogen (atmosphere), and carbon dioxide (carbonate sediments).
• Bacterial nitrogen fixation incorporates atmospheric nitrogen (N2) into the biosphere, reducing N2 to amino compounds.
• The biosphere releases nitrogen to the atmosphere via anaerobic bacterial denitrification.

Atmospheric Composition Table

• Shows the composition of dry, unpolluted air at sea level:
  • Nitrogen: 78.08% volume, 780,800 ppm concentration
  • Oxygen: 20.95% volume, 209,500 ppm concentration
  • Argon: 0.93% volume, 9,300 ppm concentration
  • Carbon Dioxide: 0.0417% volume, 424.6 ppm concentration
  • Neon: 0.0018% volume, 18.0 ppm concentration
  • Helium: 0.000524% volume, 5.2 ppm concentration
  • Methane: 0.0002% volume, 1.7 ppm concentration
  • Krypton: 0.00011% volume, 1.1 ppm concentration
  • Nitrous Oxide: 0.00003% volume, 0.3 ppm concentration
  • Hydrogen: 0.00005% volume, 0.5 ppm concentration
  • Ozone: 0.000004% volume, 0.04 ppm concentration
  • Xenon: 0.0000087% volume

Oxygen (O2)

• Generated by carbon dioxide (CO2) assimilation by phytoplankton (photosynthesizing microscopic organisms) and green plants.
• O2 has evolved alongside the biosphere's development.
• The near-balance of O2 production & consumption leaves a small amount of organic material escapes re-oxidation by marine sediment incorporation.
• Atmospheric oxygen is the excess untouched by oxidizing organic carbon and reduced chemical compounds.
• Seawater readily absorbs carbon dioxide.

Carbon Dioxide (CO2)

• Atmospheric is in equilibrium with that in the ocean (~1,000 years).
• The majority of CO2 released by thermal outgassing has entered sediments as limestone deposits.
• CO2 exchanges with the biosphere via photosynthesis and re-oxidation of organic material (10–100 years).
• The post-industrial revolution increase is caused by fossil fuel combustion.
• Record annual average atmospheric CO2 levels: 424.61 ppm in 2024.
• Monthly atmospheric CO2 concentrations peaked in June 2025 at 426.91 ppm.

Rare Gases and Trace Gases

• The isotopes have resulted from planetary outgassing.
• 40Ar, the argon isotope, is a product of potassium-40 radioactive decay.
• Trace gases don't affect air bulk composition and their local abundance is quantified by their molar mixing ratio (the chemical amount fraction), thus, excluding H2O influence.

Radicals in the Atmosphere

• The presence of radicals, such as hydroxyl radical (OH), are reported in number concentration.
• Atmospheric chemistry is largely conducted by trace gases as major air components are chemically inert.
• Atmospheric trace gas concentrations adjust to a steady state.

Adjusting to Steady State

• The adjustment to steady state relates to sources, sinks, and global distributions.
• Long-lived trace gases (2+ year residence times) achieve uniform mixing ratio.
• Short-lived trace gas mixing ratio is affected by local sources/sinks and undergoes significant variations.
• The global distribution of sources and sinks is important.
• Advection (transport by bulk motion) with winds is essential.

Major Air Pollutants

• Air pollutants technically are any atmospheric components exceeding normal concentrations.
• A pollutant is a harmful substance to human, animal, or plant health.
• Air pollutants comes in are gaseous or particulate forms.
• Pollutants enter atmosphere naturally (volcanoes, dust storms, forest fires) or anthropogenically.
• Anthropogenic sources are subdivided into stationary (point) and area or mobile linear sources.
• Point sources include stacks, flues, and chimneys.
• Area sources are groupings of small sources like industrial and steel works or combined domestic heating.
• Mobile sources include cars, planes, ships, and trains.
• Line sources are pollution emanated from a linear direction- road/aircraft.

Natural Air Pollution

• Natural pollution includes particulates like pollen and dust clouds.
• Volcanic eruptions produce fine ash dust clouds (Icelandic volcano eruption, April 14, 2010).
• Volcanic dust clouds have crystalline silica.
• Ash clouds from Eyjafjallajökull drifted over Europe in 2010, forcing airspace closures.
• The ash particles could damage engines and cause failure.

Indoor Air Pollution

• Indoor air pollutants impact health as people spend 90% of their time indoors.
• CO and NO2 come from gas heaters and cookers.
• CO and benzene (C6H6) come from cigarette smoke.
• VOCs come from synthetic furnishings, vinyl flooring, and paints.
• Biological pollutants consist of dust mites and mould

Regulated and Unregulated Air Pollutants

• Division is based on environmental agencies in the United States, the European Union, and major Asian countries.
• Regulated pollutants:
  • Sulphur dioxide (SO2)
  • Nitrogen oxides (NOx)
  • Carbon monoxide (CO)
  • Trace metals (lead (Pb), cadmium (Cd), and platinum (Pt))
  • Organic compounds (benzene and poly-aromatic hydrocarbons (PAH))
  • Photochemical oxidants (ozone (O3) and peroxyacetyl nitrates (PAN))
• The wide range of sizes for particulate matter (0.01 µm - >100 µm).
• Particulates have organic or inorganic parts.
• Types of considered include “total suspended particulates smoke and particles of a specific size (PM10 and PM2.5).
• Examples of unregulated air pollutants include carbon dioxide (CO2) and nitrous oxide (N2O).
• The proportions in Table 1.2 are for dry air, i.e. without water vapor.

Water in the Atmosphere

• The listed gases have long atmospheric residence times, well mixed and broadly the same concentrations everywhere in the atmosphere.
• Water differs due to its properties at normal temperatures and pressures.
• Only material present in all three phases – solid (ice), liquid and gas (water vapour).
• Continuous transfer between the three phases depending on the conditions.
• In contrast to the abundance of H20 liquid N2 & O2 would garner more attention.

Water Vapour

• Water vapour proportions depend on local conditions and air history.
• Air temperature determines maximum presence of water vapor.
• Water vapor is called is the saturated vapor pressure (SVP) that depends on temperature.
• Ambient vapor pressure (ea) ranges from zero up to saturated value (es).
• The ratio of actual to saturated vapor pressure is relative humidity (hr).
• Increased vapor pressure is limited by the vapor pressure will increase towwards es, but cannot exceed it.
• If the cooling occurs because the air is close to a cold ground surface, then dew results.

Summary

• Vapor concentrations max out in the humid tropics (30 °C & 100% humidity).
• Vapour pressure would be 4300 Pa (4.3% mixing ratio).
• At the low hr of 50% at −20 °C it corresponds 0.1% mixing ratio.
• Global mixing ratio is ~1% like argon abundance.

Measuring Atmospheric Composition

• The Système International d'unités, SI replaced all systems to describe measurements.
• SI has 7 base units, each having its own dimension: length, mass, time, thermodynamic temperature, amount of substance (chemical amount), electric current, and luminous intensity.
• The other quantities are derived quantities. SI units are recommended, some non-SI units are required ie. time periods (minute, hour) - hard to express in seconds.
• Conversion rule to SI units is indicated- 1 atm = 101325 Pa.

Atmospheric Compound Composition Measurement

• Concentration of particular elements
• Time over which the presence of an element is measured.
• The concentration units have number of ways to measuring.

Measuring Gaseous Pollutants

• Mass of gaseous pollutant per unit volume of air (µg m-3)

• Volume of gaseous pollutant per unit volume of air (µl l-1)

• Volume mixing ratio ( parts per million, 106), ppb (parts per billion, 109)

• Measurement is not expressed in terms of ppt (parts per trillion, 1012)

• Particulate pollutants are often measured only in mass of pollutant per unit volume of air.

• The mixing ratio is atmospheric chemistry measures the ratio of the substance.

• Concerned to volume of the substance (gaseous) in the volume of air.

• The specific mixing ratio over concentration is the mixing ratio doesnt change as a result of pressure or temperature.

• Chemical amount and volume fraction are practically identical because sir is essentially an ideal gas.

• The inter-conversion btw volume mixing ratios and mass per unit volume requires explanation.

• The atmospheric volume of gaseous air pollutants is tiny, resulting in a “perfect” or “ideal” gas.

Key Qualities of an Ideal Gas

• Molecules occupy negligible volume and exert no force.
• Volume mixing ratio isnt determined by atmospheric pressure.
• However, mass per unit volume is depending on temperature and temperature .

Key Measurement Factors

• The pressure volume for must incorporate factors.
• Atmospheric pressure and temperature has been assumed.
• Time measurement affects the pollution.
• Hourly, daily and concentrations define the air standards.

Averaging Time

• The averaging time selected for use depends upon pollution's attributes.
• Pollutants like e.g ozone which rise causes damage will cause shorter time averages.
• Seasonal average is used (Winter is = October to March, Summar = April to September.

Classification of Air Pollutants

• Health/environmental follow 3 processes: Emissions-> Transport-> Pollutant deposition.
• Pollutant classification comes from origins and effects, which includes measured emissions.
• Formation determines air pollutant types.
• Primary pollutants are emitted into atmosphere, such as CO from fuel and SO2 from power plants.
• Secondary pollutants result from chemical reactions with pollutants and atmospheric gases eg. ozone.

Note

• Pollutants fall into both primary and secondary- NO2 from power plants, vehicles and oxidation.
• Classification will help understand atmospheric pollution.
• Primary pollutants typically have proportional relationships.
• Reductions of precursors of secondary pollutants doesn't translate reductions in concs.

Air Pollutant Sources

• Definite air pollutant sources can be identified and are are classified as natural vs manmade (anthropogenic.

Natural vs. Man-Made Sources

• Natural includes volcanic erruptions, sand storms, ligntning and forest fires.
• Man Made comes from combustion for energy particulary motor vehicles/Power.
• There are non combustion such as gas leakage and methane.

Anthropogenic Pollution

• Broken down Geo Distribution can be broken to 3:
• Point- emitters whos Large enough on emissions large enough on there own (coal)
• Area collectiveley Dispered and collectiveliy
• Line sources: Source is uniformily distributed

Note

• Line with area can very some what by city. Levels can grouped acourding their Source can is used to idetify their way and make estimate level. Estimateing emissions is demanding and timing and
• The systematic compilation of detailed info gives a clear image of Given data

Emissions Inventories

• Inventory is air poluttion. amount the polution release to average amount and transports

Note

• There is impractical. Majority data from other
• Information from fuel and kilometers etc from activity date for estimating. Emission is related to the amount made to make amount material produced Here is PEC important for order to the the mass of emitted Diesel

Emission Units

-Units varies and convenient. -NOx is terms of NO2 -SDx is terms of SOx s SO2

• PCDD accounting of TOx
• Polution for full pulation and N content

UN and EU

• The nation colletivily polution
• Applicaliton to tocal
• Estmiate mad of
• Publishes datsbase that comilation list whiting warea to esitmate to desicle more
• Tese types from line and pont