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I. AIR 2 AIR POLLUTION SOURCES AND IMPACTS 2.1 ANTHROPOGENIC SOURCES OF AIR POLLUTION Stationary, mobile, fugitive, and non-fugitive Almost all human activities generate air pollutant emi...

I. AIR 2 AIR POLLUTION SOURCES AND IMPACTS 2.1 ANTHROPOGENIC SOURCES OF AIR POLLUTION Stationary, mobile, fugitive, and non-fugitive Almost all human activities generate air pollutant emissions. In cities and other densely populated urban areas, air pollution is mainly due to anthropogenic sources, which may be classified as: a) Stationary sources: Includes combustion processes (e.g., power plants and industrial boilers), chemical processes (e.g., petroleum refining and organic liquid storage), mineral processes (e.g., hot mix asphalt, cement manufacturing and concrete batching), metallurgical processes (e.g., iron and steel production), waste disposal facilities (e.g., municipal/sewage sludge/medical waste incinerators) and VOCs emitting processes (e.g., graphic printing, surface coating). There are also facllities other small but widespread sources, e.g., restaurants and food cooking which could be major local air pollution and nuisance concerns due to the excessive emissions of cooking fumes and odour. In Hong Kong, electricity generation is the most important stationary source, accounting for about 52% of SO2, 24% of NOx, 13% of PM10, and 11% of PM2.5 emissions in 2020. This copy is issued to Lau Chin Tung b) Mobile sources: Includes vehicles, trains, aircrafts, vessels, and non-road mobile machinery, etc. Emissions of NOx and PM from diesel engines are of main concern. In Hong Kong, vessels are the biggest emission sources, accounting for about 39% of SO2, 36% of NOx and 29% of PM10, 35% of PM2.5 and 37% of CO emissions in 2020. Vehicles are responsible for about 1% SO2, 19% of NOx, 10% of PM10, 11% of PM2.5 and 47% of CO emissions in the same year. The air pollutant emissions changes of Hong Kong from anthropogenic sources over the last three decades are presented in Table I-4 below. Table I-4: Change of air pollutants emissions in Hong Kong from anthropogenic sources in tonnes Air Pollutants 2000 2010 2020 Particulate matters RSP (PM10) 6090 6,310 2,930 FSP (PM2.5) 4,780 5,000 2,290 Sulphur dioxide 79,530 36,310 4,940 Nitrogen oxides 107,080 109,100 56,680 Non-Methane VOCs 30,830 32,000 21,910 Carbon monoxide 80,690 85,600 57,810 * Does not include emissions from hill fires Air pollution sources may also be grouped as point sources (i.e., stationary source with significant emissions), area sources (i.e., a number of small stationary, including domestic and commercial enlarge sources, and mobile sources that may have enormous effect collectively over an area). Air pollutants may also be emitted from sources without well-defined exhausts, e.g., dust emissions from construction activities, paved and unpaved roads; VOCs leakage from vents, valves, flanges from oil depots; odour from landfills. They are referred to as fugitive sources. V.2024.05.10 Page 15 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 2.2 NATURAL SOURCES OF AIR POLLUTION Volcanoes, wildfires, sea spray, vegetation, etc. Despite that our air pollution problem is mainly due to anthropogenic sources, most of the air pollutants are coming from natural sources. They are highly variable based on many factors including geography, season, and climatology. Examples of natural air pollution sources include: a) Dust storms (e.g., the dust storms from the Gobi Desert and northern China may transport particulates to other part of Asia, including Hong Kong which has experienced the worst dust storm incident on 21-23.3.2010) b) Vegetation, plants, and trees (e.g., isoprene, which is emitted by many tree species, especially as part of their protective measure and can contribute to O3 and secondary organic aerosol formation and pollens that induce hay fevers) c) Sea spray (e.g., sea salt aerosols) d) Wild forest fires (e.g., smoke, PM, VOCs from Australian and Californian forest fires) e) Volcano eruptions (e.g., ash, PM, acid mists, SO2, hydrogen sulphide and toxic gases) This copy is issued to Lau Chin Tung 2.3 RECEPTORS (HUMAN, ANIMAL, PLANT, MATERIALS, ATMOSPHERIC PROCESSES) A receptor/receiver is something which is adversely affected by polluted air, including human beings, animals, trees or plants, materials, and the environment as a whole. Some sub-populations are more sensitive to air pollution and they include children, the elderly, and individuals with existing illnesses (e.g., chronic obstructive pulmonary disease (COPD), asthma, pneumonia, cardiovascular disease, lung cancer). 2.4 SOURCE / RECEPTOR RELATIONSHIPS (SPATIAL & TEMPORAL) The concentration of an air pollutant is, in general, proportional to the strength of emissions. Other than O3 and secondary air pollutants which could have maximum concentrations farther away from sources, most primary air pollutants (e.g., CO, SO2, NOx) usually have higher concentrations at receptors close to the sources. In coastal urban cities like Hong Kong, motor vehicles and vessels are important sources of elevated pollutant concentrations. Receivers at busy roadsides and shorelines are having higher concentrations of associated air pollutants (i.e., NOx and PM10/PM2.5 for roadsides and SO2 and NOx for shoreline receptors). The spatial relationship between sources and sub- population of lower socioeconomic position often reflects the presence of environmental equity issues within the city. By virtue of the location of their place of residence, school, or workplace, they are often receiving higher air pollutant exposures. Temporally, the concentrations of air pollutants, other than O3 and other secondary air pollutants which may have different diurnal patterns (e.g., O3 usually peaks in the afternoon because the solar radiation intensity is the highest), follow generally the diurnal pattern of human activities and traffic. For examples, higher levels of NO2, PM2.5 and PM10 are usually observed in the morning and the evening rush hours when there are more traffic and human activities. The weekday-weekend patterns can also be associated with differences of emissions in weekdays and weekends. In addition, the V.2024.05.10 Page 16 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR difference of demands for heating/cooling over seasons also results in the seasonal changes of combustion related air pollutants, e.g., SO2, NOx. The long-term annual air quality trend often has greater association with the emission sources due to the averaging effect of the meteorological variation. It is useful in assessing the effectiveness of emission control measures on improving air quality at the affected receptors. 2.5 ADVERSE EFFECTS 2.5.1 Health effects (mortality, morbidity, respiratory illness, sub-clinical effects) Air pollution is the largest contributor to the burden of disease from the environment. The WHO estimated that ambient air pollution in 2019 was responsible for 4.2 million premature deaths. Exposure to air pollution, depending on the nature of the air pollutants (e.g., physical state, particle sizes, vapour pressure, and toxicity), susceptibility of the receptors (e.g., gender, age, and health status), and concentrations and exposure duration, can have significant impacts on human health. A This copy is issued to Lau Chin Tung broad range of adverse health effects ranging from death from respiratory diseases, stroke, heart disease, brain damage, eye irritation, to reduced quality of life, and including some irreversible changes in physiological function, have been identified to be associated with air pollution. The adverse effects can be short term (acute) and long term (chronic), resulting from short term exposure at high concentrations and long-term exposure at lower concentrations of air pollutants. The short-term adverse effects are expressed as: daily mortality, respiratory and cardiovascular hospital admissions, respiratory and cardiovascular emergency department visits, respiratory and cardiovascular primary care visits, use of respiratory and cardiovascular medications, days of restricted activity, work absenteeism, school absenteeism, acute symptoms (wheezing, coughing, phlegm production, respiratory infections), and physiological changes (e.g., lung function). Long term effects include mortality due to cardiovascular and respiratory disease, chronic respiratory disease incidence and prevalence (asthma, COPD, chronic pathological changes), chronic changes in physiologic functions, lung cancer, chronic cardiovascular disease, and intrauterine growth restriction (low birth weight at term, intrauterine growth retardation, small for gestational age). The relationship between air pollution and health is established by: a) Epidemiological studies – e.g., time series studies that estimate the influence of temporal (usually daily) variations in air pollutant concentrations on mortality or morbidity by statistical models, and cohort studies that estimates chronic effects by comparing people living in different geographical locations with different air pollution exposures. b) Toxicological studies – effects of air pollution have been generated through inhalation studies, whereby human volunteers or animals are placed under controlled exposure conditions. preventlon c) Studies of effects of air pollution interventions. hizn Some of the effects associated with the more common air pollutants are: a) CO – Reduces the oxygen carrying capacity of red blood cells. Typical symptoms of exposure to low levels of CO include headache, dizziness, and tiredness. Higher concentration of CO can lead to impaired vision, disturbed coordination and eventually death. V.2024.05.10 Page 17 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  δ ” I. AIR - b) NO2 – Irritates the mucosa of the eyes, nose, throat, and the lower respiratory tract. Exposure to low level of NO2 may cause increased bronchial reactivity and in those with asthma increased response to allergens. NO2 also aggravates existing chronic respiratory diseases. Long- term exposure to NO2 can lower a person's lung function and resistance to respiratory infections. It is responsible for the largest short-term health risks in Hong Kong and other urban areas with @ heavy traffic. c) O3 – Irritates eyes and brings upper and lower respiratory symptoms to healthy people. It may also provoke asthmatic attacks in asthmatics. O3 can also increase a person's susceptibility to respiratory infection and aggravate pre-existing respiratory illnesses. It is responsible for the largest short-term health risks in areas with little traffic, e.g., rural areas. d) Particulates – Both PM10 and PM2.5 are respirable and pose adverse health effects. The latter are more dangerous since, when inhaled, they may get deeper into the lungs. Increases in particulates concentration are associated with increases in daily hospital admissions and premature deaths from respiratory and cardiovascular diseases. Persons with pre-existing cardiovascular and respiratory diseases are most susceptible. Diesel particulates and PM have been classified as carcinogenic to humans (Group 1) by IARC. They are responsible for the largest air pollution induced cancer risk. This copy is issued to Lau Chin Tung e) SO2 – Irritates eyes and nose. Inhalation of SO2 causes narrowing of the airways (bronchoconstriction), which people suffering from asthma and chronic respiratory diseases are more sensitive to than other people. f) Lead – Highly toxic and is known to damage the nervous system and kidney and interferes with the synthesis of haemoglobin. Children are more vulnerable to the effects of lead, which can result in learning disabilities and impaired neurobehavioural functioning. g) Toxic air pollutants – TAPs pose various serious and irreversible adverse health threats to humans. Many (e.g., diesel particulates, formaldehyde, benzene, 1,3-butadiene, benzo[a]pyrene and other PAHs, dioxins, compounds of Cd, Cr(VI) and Ni) are carcinogens or suspected carcinogens. Other major health concerns include mutagenic, teratogenic, neurotoxic effects. The World Health Organization have prioritised and selected the relevant health effects/outcomes for each of the air pollutants in developing its air quality guidelines. For example, all-cause and respiratory mortality have been selected for PM2.5, PM10, O3, NO2. In addition, cardiovascular and lung cancer mortality have also been considered for PM2.5 and PM10. 12 2.5.2 Ecological impacts, vegetation, and forest deterioration Effects on vegetation The air pollution effects on plants and vegetation may be visible or nonvisible. The visible effects include the destruction of the waxy coatings on leaves or deviations in the normal healthy appearance of leaves, including tissue collapse and loss of colour. These observable alterations in the plant are termed air pollution injury. Non-visual effects involve reduced plant growth, changes in the reproductive cycle, or alteration of physiological or biochemical changes. The economic or aesthetic loss due to interference with the intended use of a plant is termed air pollution damage. The major air pollutants which are phytotoxic to plants are O3, SO2, NO2, fluorides, and PAN. 12 World Health Organization, WHO global air quality guidelines. Particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide, p.36-45, 2021 V.2024.05.10 Page 18 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR Effects on animals A major concern is with deposition and accumulation of airborne contaminants on vegetation or forage that serves as feed for the animals. The major air pollutants of concern include heavy metals (e.g., As, Pb, Hg) from industrial air emissions, fluoride emissions from fertilizer processing facilities, and dioxins from incinerators. Effects on forests The pollutants most often involved are SO2 and hydrogen fluoride. Historically, the most harmful sources of pollution for forest ecosystems have been smelters and aluminium reduction plants. The impact of acid deposition on forests depends on the quantity of acidic components received by the forest system, the species present, and the soil composition (e.g., alkalinity). Materials corrosion The major effects of air pollutants on materials include: a) Metal: corrosion of the surface, loss of metal, tarnishing by SO2 and other acidic gases b) Building materials: discoloration, soiling of surfaces, leaching of metals, and affecting the integrity of the structures by SO2, acidic gases, sticky particulates This copy is issued to Lau Chin Tung c) Monuments: deterioration of stone or marble structures by SO2 and other acidic gases d) Paint: discoloration, softening of finishes by SO2, H2S, sticky particulates e) Leather: powdered surface, weakening by SO2 and other acidic gases f) Paper: embrittlement by SO2 and other acidic gases g) Textiles: loss of tensile strength, spotting by SO2 and other acidic gases h) Dyes: fading, yellow discoloration by NO2 and oxidants i) Rubber: cracking, weakening by O3 and oxidants j) Ceramics: change of surface appearance by acidic gases Lake acidification Acidic deposition, in either a wet or dry form, contributes to the changes of the acidity in soil, lake and fresh water. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. In watersheds with low alkalinity soil, lakes and streams are susceptible to low pH and leaching of aluminium, calcium, magnesium, sodium, and potassium from the soil into surface waters. This combination has been found to be very toxic to some species of fish. When the pH drops to >5, many species of fish are no longer to reproduce and survive. Another area of concern of fresh water or lake acidification is reduced tree growth in forests. As acidic deposition moves through forest soil, the leaching process removes nutrients. If the soil base is thin or contains barely adequate amounts of nutrients to support a particular mix of species, the continued loss of a portion of the soil minerals may cause a reduction in future tree growth rates or a change in the types of trees able to survive in a given location. 2.5.3 Others Visibility Visibility is the maximum distance at which a dark object can be observed against a bright background. Visibility impairment, or reduced visibility, which is the degradation of the ability to perceive the environment, is the most recognizable effect of air pollution. It is caused by the light extinction in the atmosphere as a result of light scattering and absorption by water vapour (humidity) and gaseous air pollutants (e.g., NO2, O3) and particulates (PM2.5; those with 0.1-1 µm in size are most effective at scattering light). In Hong Kong, it has been shown that ammonium sulphate, organic C, and elemental C in the PM2.5 are the more important contributors to visibility degradation. V.2024.05.10 Page 19 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR Quantitatively, visibility impairment is often referred to visibility below 8 km when the relative humidity is below 95% and there is no fog, mist, or precipitation. Due to the previous air pollution control efforts, the number of hours of reduced visibility observed in Hong Kong had been improved to 401 hours in 2022 from the worst of 1,570 hours in 2004. Odour Some air pollutants are odorous. Nuisance is the primary effect and the factors relevant to perceived odour nuisance are: a) Its offensiveness b) Duration of exposure c) Frequency of occurrence d) Tolerance and expectation of the receptor Some odourous pollutants (e.g., H2S, O3) can cause adverse health effects and for others, even they are not causing direct damage to health, they may give rise to nausea, insomnia, and discomfort. Very strong odour can result in nasal irritation, and/or can trigger symptoms in individuals with asthma or other breathing problems. This copy is issued to Lau Chin Tung 2.6 HEALTH IMPACT ASSESSMENTS, ECONOMIC IMPACT ASSESSMENTS, AIR TOXICS AND RISK ASSESSMENTS Health impact and risk assessments are a combination of procedures, methods, and tools to characterise respectively the human health and environmental risks associated with exposure to pollution. The term ‘risk’ is defined as the probability of having an adverse health or environmental outcome (e.g., heart and lung diseases, or dying). The increase of risk is expressed as its relative risk (RR). It is defined as the ratio of the incidence of (or death from) a disease or environmental outcome, in a population group that is exposed to air pollution compared to the incidence in a group that is not exposed to air pollution. Excess risk (ER) is defined as RR -1 and is usually expressed as a percentage. Another measure of the importance is the ‘attributable fraction’, which is equal to (RR-1)/RR. Typically, these assessments evaluate the impact of existing level of pollution and/or the effects of an air quality improvement policy or programme. The assessment involves the estimation of the total number in the population who developed health effect (ΔH) associated with the air pollutant exposure. ΔH = H (RR – 1) = H (exp(β ΔC) – 1) where: H = baseline number in the population who developed the health effect (i.e., baseline incidence rate x population) RR = the relative risk of developed health effect associated with the air pollutant exposure β = dose response coefficient of the health effect per unit change of air pollutant concentration ΔC = change in air pollutant concentration The economic impact assessment of an air quality improvement policy or programme is a combination of procedures, methods, and tools which aims to evaluate its cost and the economic impact of and quantify the economic value of its benefits. In addition to the costs (including capital costs and operating costs of air pollution mitigation and other social costs), the other important element of the assessment is the quantification of the health impacts. V.2024.05.10 Page 20 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR In general, health costs can generally be taken as the sum of the costs of mortality and morbidity. For the former, there are two approaches in quantifying the cost of mortality: i. The value of statistical life (VSL), which is derived from aggregating individuals’ willingness to pay (WTP) to secure the reduction in the risk of premature death (e.g., US$7.9 M (in 2008 dollars) in USA) ii. The value of a statistical life-year (VSLY), which estimates the values for a year of statistical life rather than life (in practice, it is often derived by dividing the VSL by remaining life expectancy) The respective epidemiological parameters used in calculating the economic cost are excess premature deaths and year of lives lost (YLL), respectively. The costs of morbidity include: a) Resource costs – e.g., the direct medical and non-medical costs associated with treatment for the adverse health impact of air pollution, plus avertive expenditures) b) Opportunity costs – e.g., those associated with the indirect costs related to loss of productivity and/or leisure time owing to the health impact c) Dis-utility costs – i.e., those related to the pain, suffering, discomfort, and anxiety linked to the This copy is issued to Lau Chin Tung illness Among others, the excess hospital admission and years lived with disability (YLD) are the more common epidemiological parameters of morbidity used in the assessment. V.2024.05.10 Page 21 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 3 AIR POLLUTION MODELLING 3.1 PURPOSES OF AIR QUALITY MODELLING Air quality modelling uses mathematical and numerical techniques to simulate the physical and chemical processes that affect air pollutants as they disperse and react in the atmosphere. These models are important to an air quality management system and have been widely used to: a) Simulate ambient pollution concentrations under different scenarios b) Determine the relative contributions from different sources c) Augment the air quality monitoring for assessing the air quality standard compliance status d) Support real-time air pollution forecasting as routine operation and/or during episodes e) Support environmental impact assessment (EIA), plant siting and regulatory requirements 3.2 LEVELS OF MODELLING EFFORT This copy is issued to Lau Chin Tung Air quality modelling may involve two levels of sophistication. The first level consists of the use of relatively simple screening models to provide conservative estimates of the air quality impact of the sources. The purpose is to eliminate the need of more detailed modelling for those sources that clearly will not cause significant impacts on air quality. The second level involves the use of refined models with more refined inputs and detailed treatment of physical and chemical atmospheric processes. They need to be use for proper air quality assessment, planning and compliance evaluation. Air quality models may also be grouped as regulatory models and research models. The former are accepted for regulatory air quality assessments to ensure consistency. The latter are useful for air quality forecast and other scientific applications given their better air quality prediction accuracy. 3.3 TYPES OF AIR POLLUTION MODELS 3.3.1 Box, Gaussian dispersion Box Model The box model is the simplest of the models by assuming the volume of atmospheric air is in the shape of a box and that the air pollutants inside the box are homogeneously distributed. The steady state concentration is given by: C = Q × L / (H × u) where: Q = emission rate (g/s) H = height of the box (mixing height) (m) L = distance over which the emission takes place (m) u = mean wind speed (m/s) V.2024.05.10 Page 22 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR mormstribution Gaussian Dispersion The Gaussian dispersion model provides a simple solution to the dispersion (transport and diffusion) equations for constant emissions under steady-state meteorological conditions. It assumes that: a) Atmospheric stability and all other meteorological parameters (e.g., wind speed and direction) are uniform and constant throughout the layer into which the pollutants is discharged b) Turbulent diffusion is a random activity and therefore the pollutant concentrations can be taken as normally distributed in a bell-shaped curve about the plume centre line c) Pollutant is released at an effective stack which is the sum of the physical stack height and plume rise due to its momentum and buoyancy d) The degree of dilution is inversely proportional to the wind speed e) Pollutant material reaching the ground level is reflected back into the atmosphere f) The pollutant is conservative, i.e., not undergoing any chemical reactions, transformation or decay It can be described by the following equation: 2 2 2 −1 𝑦𝑦 −1 𝑧𝑧−𝐻𝐻 −1 𝑧𝑧+𝐻𝐻 Q 𝐶𝐶(𝑥𝑥, 𝑦𝑦, 𝑧𝑧, 𝑡𝑡) = 𝑒𝑒 2 𝜎𝜎𝑦𝑦 𝑒𝑒 2 𝜎𝜎𝑧𝑧 + 𝑒𝑒 2 𝜎𝜎𝑧𝑧 2πu𝜎𝜎𝑦𝑦 𝜎𝜎𝑧𝑧 This copy is issued to Lau Chin Tung where: C(x,y,z) : pollutant concentration at point (x,y,z) u: wind speed (in the x "downwind" direction) σy, σz: the standard deviation of the concentration in the y and z direction Q is the emission strength H is the effective stack height The standard deviations are dependent on atmospheric stability and distance from the source. The equation can be spatially integrated to simulate the effects of line, area, and volume sources. Gaussian dispersion models commonly used by the modelling community are: (i) AERMOD developed by USEPA; (ii) CALINE-4 developed by the Department of Transportation of California, USA for modelling vehicular emission impacts; and (iii) ADMS developed by CERC in UK. 3.3.2 Photochemical Photochemical models simulate the changes of pollutant concentrations in the atmosphere over large spatial scales using a set of mathematical equations characterizing the chemical transformation (gas and aqueous phase and heterogeneous chemistry) and physical processes (horizontal and vertical advection and diffusion) and removal process (dry and wet deposition) in the atmosphere. Depending on the frame of reference, photochemical air quality models may take the form of a Lagrangian trajectory model that employs a moving frame of reference, or the Eulerian grid model that uses a fixed coordinate system with respect to the ground. Lagrangian models keep track of the movement of a large number of air parcels carried by the wind along trajectories. They simulate pollutant concentrations inside the air parcels at different locations at different times. Eulerian models allow air pollutants enter and leave each grid cell and simulates the concentrations at all locations as a function of time. Lagrangian models are computationally simple but the physical processes they can describe are somewhat incomplete. On the other hand, Eulerian models are more capable of accounting for topography, atmospheric thermal structure, physical processes, and reactive pollutants from many sources. Most of the current operational photochemical models have adopted the three- dimensional Eulerian grid modelling approach. V.2024.05.10 Page 23 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR The photochemical grid model simulates the atmosphere by dividing it into thousands of individual grid cells (e.g., 1 km x 1 km with thickness varying from less than 20 m near the ground to a few km at the higher levels of the atmosphere). Driven by a meteorological model that is similar to those used for weather forecasting, the winds that carry pollutants around the city are first accurately characterised. The model calculates concentrations of air pollutants, such as secondary particulate matter, secondary gaseous pollutants such as O3 and NO2, in each cell by simulating movement of air into and out of cells (advection and dispersion); mixing of air pollutants upward and downward among layers; injection of new emissions from sources such as point, area, mobile, and biogenic into each cell; and chemical reactions based on chemical equations, pollution precursors, and incoming solar radiation in each cell. The two photochemical models most used by the air quality modelling community are (i) Comprehensive Air Quality Model with Extensions (CAMx); and (ii) Community Multiscale Air Quality (CMAQ) Modelling System. 3.3.3 Physical, CPD models Physical Model This copy is issued to Lau Chin Tung Physical modelling involves the simulation of the physical process on a smaller scale in the laboratory by the use of wind tunnel or other fluid modelling facilities. Because of the complexity and high construction and operational cost, physical model will only be used for dealing with complex flow situation, such as building, terrain, or stack downwash conditions, plume impact on elevated terrain, diffusion in an urban environment or complex terrain. Computer Fluid Dynamics Model Computer fluid dynamics (CFD) modelling aims to solve the partial differential equations representing atmospheric dispersion phenomena by numerical integration techniques and provide wind fields at high grid resolution. CFD models are capable to deal with very complex building shapes and boundary conditions at fine grid down to meter scale. CFD codes are structured around numerical algorithms that can tackle fluid flow problems. Most commercial CFD packages contain three main elements: i. The pre-processor, which serves to input problem parameters, generate the grid of computational domain, select the physical and chemical phenomena that needed to be treated, define the fluid properties, and specify the appropriate boundary conditions ii. The solver, which first approximates numerically the unknown flow variables, then discretizes the governing flow equations using these approximations, and finally solves the resulting system of equations iii. The post-processor, which displays the grid and geometry of the domain, plots wind vectors and pollutant concentration contours and provide animation facilities for dynamic result display In Hong Kong, CFD is one of the tools being used for assessing of the effects on air ventilation from major development or redevelopment proposals in accordance with the Technical Guide for Air Ventilation Assessment for Developments in Hong Kong to prevent stagnant or slow air movements in streets and urban spaces. V.2024.05.10 Page 24 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 3.3.4 Receptor models Receptor models are mathematical or statistical procedures for identifying and quantifying the sources of air pollutants at a receptor location. Unlike photochemical and dispersion air quality models, receptor models do not use pollutant emissions, meteorological data, and chemical transformation mechanisms to estimate the contribution of sources to receptor concentrations. Rather, they use observational data and rely on the different chemical signatures of gases and particles measured at source and receptor to both identify the presence of and to quantify the relative importance or contributions of the sources to receptor concentrations. Common receptor models include: a) Chemical Mass Balance (CMB) It uses source profiles and speciated ambient data to quantify source contributions. Contributions are quantified from chemically distinct source-types rather than from individual emitters. Sources with similiar chemical and physical properties cannot be distinguished from each other by CMB. b) Positive Matrix Factorization (PMF) The PMF technique is a form of factor analysis where the underlying co-variability of many variables (e.g., sample to sample variation in PM species) is described by a smaller set of factors This copy is issued to Lau Chin Tung (e.g., PM sources) to which the original variables are related. 3.4 EMISSION INVENTORY AND EMISSION MODELLING Emissions inventory is the estimates of the emissions from various pollution sources in a geographical area. The typical emission categories include: Stationary source – (a) Point sources, i.e., those with well-defined emission exhaust and location with significant emissions; (b) Area sources: those stationary sources, including residential and fugitive emissions, that are too small or too spread out to be classified as a point source Mobile Sources – (a) on road vehicles; (b) non-road mobile machinery; (c) marine; (d) aviation Natural Sources – e.g., biogenic emissions It helps the regulatory authority to determine significant sources of air pollutants and to target regulatory actions. The emission trends over time, which reflect the effectiveness of the control actions, can be established with periodic updates of the emissions inventory. Emissions inventories are an essential input to mathematical models that estimate air quality. The effect on air quality of potential regulatory actions can be predicted by applying estimated emissions reductions to emissions inventory data in air quality models. In Hong Kong, the EPD compiles and reports the Hong Kong Air Pollutant Emission Inventory annually. Methods to determine emissions include continuous monitoring of emissions from a source and use of emissions factors. The latter is a representative value that attempts to relate the quantity of a pollutant emitted with an activity level (e.g., kg of particulate emissions per Mg of coal burned) associated with the emission of that pollutant. Useful compilations of emission factors include the USEPA’s AP-42 13. 13 https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors V.2024.05.10 Page 25 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR The general equation for emissions estimation is: E = A × EF × (1 – C × RE) where: E = emission estimate for the process A = activity level such as throughput (maximum continuous rating x load factor x activity hours) EF = emission factor assuming no control C = control efficiency RE = regulatory effectiveness, an adjustment to C to account for failures and uncertainties that affect the actual performance of control Emission inventories (e.g., Hong Kong’s Emission Inventory) are usually presented as the sum of the emissions within the same source category although additional information would also be available for major point sources. In air quality modelling applications, higher resolutions, both spatially and temporally are needed. Emission modelling techniques are used to disaggregate and resolve the emissions spatially, e.g., by geographical information such as population densities, land use and other data, and temporally, e.g., the activity pattern, traffic intensities (rush hours, weekends and working days, summer and winter driving patterns, etc). This copy is issued to Lau Chin Tung Among other sources, estimating the type and quantity of contaminants emitted from roadways is inherently complex because emissions vary according to many factors including: a) Travel Related Factors – e.g., the number of trips, distance travelled and driving mode (idling, cruising, acceleration and deceleration, traffic volume, traffic condition, speed, engine load of the vehicle b) Road Network Related Factors – e.g., the geometric design features of the roads such as grade, signalized intersections, freeway ramps, toll booths, weaving sections c) Vehicle Related Factors – e.g., engine types and sizes, horsepower, weight, and age of the vehicles The on-road vehicle emission model used in Hong Kong is the EMFAC-HK14. It calculates the vehicular emission inventories for hydrocarbons (which can be expressed as TOG (total organic gases), VOC, total hydrocarbon, or methane), CO, NOx, CO2, and particulate matters (PM10, PM2.5). 3.5 MODEL LIMITATIONS, ASSUMPTIONS, ACCURACY The uncertainty involved in the air pollution modelling simulation arises from factors including (i) the input data errors (meteorology and emission-related parameters, etc.) and in the model itself, (ii) model uncertainties including uncertainties in parameters like chemical rates, uncertainties in the science on which the model is based, and (iii) uncertainties in transforming the science into numerical form. For example, as the Gaussian models assume the air pollutants are chemically inert, the terrain is not steep or complex and the meteorology is uniform spatially; they ignore changes in wind speed and directions and obstacles in real world; they cannot be used during calm wind situation and are usually only applicable to near-field (within 10 km from the source) calculations for screening purposes. Many model characteristics, e.g., land-use characteristics, boundary layer formulation, cumulus parameterization scheme, cloud microphysics, will significantly affect the model results. Inaccuracy in the simulation of these characteristics will contribute to the performance of the models. The use of emission inventories that are out of date or based on uncertain emission factors and activity levels are 14 https://www.epd.gov.hk/epd/english/environmentinhk/air/guide_ref/emfac-hk.htm V.2024.05.10 Page 26 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR often another major sources of model errors. Also, the site-by-site air pollutant concentrations predicted may also not be accurate due to small-scale weather and emission features that are not captured in the model. The confidence in model’s performance is gained by rigorous comparison with monitoring data. 3.6 SOURCE / RECEPTOR RELATIONSHIPS Commonly used air quality models (except receptor-oriented models such as CMB, PMF mentioned above and source apportionment techniques that analyse the chemical composition of air pollutants (e.g., PM10, PM2.5, VOCs) to identify and quantify sources at the receptors) are emission based or source oriented. Emission-based models use best estimates of the emission rates from various sources and of the meteorology to estimate the concentration of various air pollutants at various receptors. Emission-based models are suitable for estimating the effects of sources, e.g., in the licensing process and EIA for new sources, understanding the causes of air pollution episodes, estimate the relative This copy is issued to Lau Chin Tung contributions of different sources, air quality forecasting and estimation of the effectiveness under different source emission control options. In Hong Kong, assessing air quality impacts from new sources of a proposed project follows a three- tier approach that focuses on the following emission sources: Tier 1 – Primary contributions: the project-induced emissions, including emissions from the process of the proposed project and/or its induced traffic (e.g., a residential development leading to an increase in traffic volume in the nearby road network; the change in traffic distribution of new or enhanced road projects). Tier 2 – Secondary contributions: emissions from pollutant emitting activities with notable impacts in the immediate vicinity of the proposed project (usually, within 500 m of the proposed project site boundary), contributing further to local air quality impacts. Tier 3 – Background contributions: Those sources that are not covered by the two preceding contributions. Background contributions are usually accounted for by the spatially averaged concentrations of regional air quality models (e.g., PATH) at a certain spatial resolution (e.g., 1 km x 1 km). The air quality impacts of the emission sources of all the three tiers will be added up to give rise to the overall air quality impacts. For the purpose of determining compliance with the Hong Kong Planning Guidelines, any domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, place of public worship, library, court of law, sports stadium, or performing arts centre shall be considered to be a sensitive receptor. Three source-oriented models as shown in Table I-5 below are currently accepted by the EPD although the use of other models may be accepted according to their technical details and performance. V.2024.05.10 Page 27 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR Table I-5: Source-oriented models accepted by the EPD Model Type Source Application (a) CALINE 4 Gaussian plume Department of For mobile traffic emission impacts type Transportation, (line sources) California, USA (b) AERMOD Steady-state USEPA For point, area, and volume dispersion model sources (c) PATH v2.1 Grid-based HKEPD Provide meteorological data to comprehensive drive CALINE 4 and AERMOD, modelling system provide air pollutant concentration estimates for Tier 3 background contribution The PATH v2.1 (Pollutants in the Atmosphere and their Transport over Hongkong - version 2.1) is set up on a three-dimensional grid system with horizontal nesting. The most commonly used horizontal domain currently has grid spacing of 1 km in both the N-S and E-W direction. The thickness of the first This copy is issued to Lau Chin Tung model layer can be taken to be 17 m. The relevant outputs are the gridded meteorological and pollutant concentration data every hour of the simulation period. Similar to other modern air quality modelling system, in addition to the setting of the initial conditions for the model parameters, the PATH v2.1 system consists of three major modules which require different input data: i. Meteorological module The Weather Research Forecast (WRF) model is the meteorological software used in PATH v2.1. It requires input data as (i) upper air and surface observations, including wind, temperature, relative humidity, sea-level pressure, and sea surface temperature, (ii) global model and other regional model's output as lateral boundary conditions, and (iii) topographic and land use data. The system generates meteorological output data required by the emission and chemical transport modules. ii. Emission module Anthropogenic and natural emission inventory data are processed in the emission modelling system. The Sparse Matrix Operator Kernel Emissions (SMOKE) and the Model of Emissions of Gases and Aerosols from Nature (MEGAN) are used. iii. Chemical transport module CMAQ is the Chemical Transport Models (CTMs) used for transport and chemistry simulation. Balancing the need for representativeness with the resource demand for long-term simulations, EPD accepts a minimum of one-year simulation of air quality on an hour-by-hour basis for environmental impact assessment. V.2024.05.10 Page 28 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR To help air quality professionals conduct assessments of the resulting air quality from air sensitive receivers by air pollution dispersion modelling, EPD has prepared the following documents: 15,16 Guidelines on Assessing the ‘Total’ Air Quality Impacts Guidelines on Choice of Models and Model Parameters Guidelines on the Use of Alternative Computer Models in Air Quality Assessment Guidelines on the Estimation of 10-minute Average SO2 Concentration for Air Quality Assessment in Hong Kong Technical Notes on Air Quality Modelling Guidance Note on Specified Process Licence Applications 3.7 AIR QUALITY FORECASTING In air quality forecasting, the forecasters use a variety of data products, information, tools, and their own experience to predict air quality. Among others, multi-linear regression has been used to forecast air pollution for the purpose of alerting the population. This copy is issued to Lau Chin Tung C = c1V1 + c2V2 ……. cnVn + constant where: C = predicted air pollutant concentration c = coefficients (weighting factors) V = predictor variables (e.g., forecasted precipitation, maximum and minimum temperatures, wind speeds, relative humidity, previous day’s concentration, day of week / holiday factor, etc.) Other statistical techniques have also been used. Three-dimensional air quality models that simulate the physical and chemical processes that result in the formation and destruction of air pollutants, may be extended to a forecast mode to predict air quality. In some regulatory authorities, an ensemble of many air quality models has been used to give on average better performance than individual models for air quality forecasts. As air quality models can forecast for a large geographic area, including those areas where no air quality measurements are conducted, the forecasts can be presented as maps of predicted air quality in Apps of mobile phone to better inform the public on how predicted air quality varies hour by hour. Such practice has already been implemented in some countries or economies (e.g., London). 15 https://www.epd.gov.hk/epd/english/environmentinhk/air/guide_ref/guide_aqa_model.html 16 Guidance Note on Specified Process Licence Applications and Assessment of the Resulting Air Quality https://www.epd.gov.hk/epd/sites/default/files/epd/english/environmentinhk/air/guide_ref/files/GNSPLAARAQ.pdf V.2024.05.10 Page 29 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 4 AIR QUALITY MANAGEMENT STRATEGIES 4.1 AIR POLLUTION PREVENTION VERSUS CONTROL The main purpose of air quality management (AQM) is to protect public health and the environment from the adverse effects of air pollution. The best strategy is prevention, which may involve (i) reducing polluting activities; and (ii) sustainable energy policy promoting the use of cleaner fuels or renewable energy, energy efficiency, energy and resources conservation, land use planning, transport planning, sustainable transport measures (e.g., mass transit, pedestrian, cycling, etc.), clean production, etc. That said, emission control is very essential and necessary to achieve acceptable air quality. In the case that air pollution still remains high after control, it is necessary to implement measures (e.g., pedestrian zone, prohibition of idling vehicles, provision of timely health protection advice during air pollution episodes, etc.) to prevent or minimise exposure to air pollution. In any case, good publicity to enhance public awareness and understanding of air quality as well as public engagement are essential in gaining the public’s partnership in ensuring acceptable and sustainable air quality. This copy is issued to Lau Chin Tung 4.2 BEST PRACTICABLE MEANS AND TECHNOLOGY FORCING APPROACH The emission standard approach, which is also known as the best practicable means (BPM) approach, assumes that by rigorously requiring the maximum possible degree of emission control, the cleanest possible air will be achieved. Emission standards, which are derived from consideration of the BPM or best available control technology with or without economic consideration, are specified in terms of the maximum amount or concentration of the air pollutant which is allowed to be emitted from the source. If the control technology is still emerging, the promulgation of a set anticipated emission standards will help its early maturation and commercial application. This is often referred to as the “technology forcing approach” and has been commonly used in vehicle emission control. The advantage of this approach is its simplicity and can be implemented even without any extensive air quality monitoring or modelling. But for the same reason, it cannot guarantee that acceptable air quality will be achieved or maintained. Examples of air pollution control programmes applying this strategy include the USA’s New source performance standards (NSPS), the Best Available Control Technology (BACT) or Lowest Achievable Emission Rate (LAER) for new or modified sources respectively in attainment and non-attainment areas, the Maximum Achievable Control Technology (MACT) for prevention of TAP emissions. In Hong Kong, the control of specified processes by requiring the use of BPMs and imposition of the stringent Euro standards on vehicles are also examples of this control approach. V.2024.05.10 Page 30 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 4.3 AIR QUALITY STANDARDS APPROACH AND CRITERIA POLLUTANTS This approach first designates the level of pollution deemed acceptable, i.e., the air quality standards or objectives (AQO) and then achieves these standards through the control of the amount, location, and time of air pollutant emissions. The following seven operational stages are involved: 1. Specifying the air quality standards 2. Monitoring air pollutants concentrations to ascertain if these standards are in compliance 3. Compiling an emission inventory as the input to air quality models 4. Conducting the air quality modelling to determine the required quantity of emission reduction and predict air pollution levels arising from various emission reduction options 5. Devising an air quality management plan (AQMP) to achieve the established AQOs 6. Implementing the air quality management plan 7. Reviewing air quality monitoring results to ascertain the effectiveness of control/management efforts to determine if additional measures are required Hong Kong’s AQOs are established for 7 criteria air pollutants, namely, SO2, NO2, PM10, PM2.5, O3, CO, and Pb. Promulgation of AQOs and “Clean Air Plan for Hong Kong 2035” and the EIA process are This copy is issued to Lau Chin Tung examples of the application of this approach. The Clean Air Plan for Hong Kong 2035 17 is to set out the vision of “Healthy Living．Low-carbon Transformation．World Class”, and the challenges, goals, and strategies to enhance the air quality of Hong Kong to 2035. The following six major action areas have been identified with key measures to be taken for improving the air quality: 1. Green transport (comprising electric vehicle roadmap, environment-friendly new development areas, green transport network, new energy ferries); 2. Liveable environment (comprising city planning, health information); 3. Comprehensive emissions reduction (on vehicular emissions, vessels emissions and VOCs) 4. Clean energy (including power plant emissions reduction, green energy), 5. Scientific management (covering information dissemination and advanced monitoring); and 6. Regional collaboration (including formulation of region emissions reduction targets for 2025 and 2030, regional air monitoring and analysis, knowledge exchange) 4.4 MARKET-BASED MECHANISM, EMISSION TRADING, EMISSION OFFSETTING In the market-based approach, the regulatory authority determines the total amount of emissions to be permitted to be discharged to the air and allow the polluters to determine and implement their most cost-effective means for ensuring their total emissions will not exceed the quantity of these emission allowances. The first control application of this approach was USA’s “bubble” policy. Within an imaginary bubble, the polluter is allowed to undertake intra-company emission trading or compensate any excessive emissions from one or sources by same or greater amount of emission reduction in other sources in the same premises. This “offset” policy was subsequently extended to intra-company trading. In the full-scale emission trading (also known as “cap-and-trade programme”), the authority will issue a number of “emissions allowances” equivalent to the total amount of emissions to be permitted to be discharged to the air (usually 1 tonne per allowance), either by allocation or auction to the polluters. 17 https://www.eeb.gov.hk/sites/default/files/pdf/Clean_Air_Plan_2035_eng.pdf V.2024.05.10 Page 31 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR The allowances are tradable to enable greater compliance flexibility. To ensure effective implementation, emissions are accurately monitored (e.g., by continuous emission monitoring systems), reported and audited. The USA’s Acid Rain programme of 1982 for controlling SO2 and NOx was the first cap-and-trade programme. In Hong Kong, power plants are also permitted to use emission trading to meet the emission cap requirements. Emission tax (or pollution charge) is also considered as a market-based approach because it allows the flexibility for polluters to determine the best control option and that tax itself can be taken as an incentive to polluters to further reduce their emissions by adopting improved control technologies and practices. In this approach, air is taken as precious public resources and hence it is logical to require the polluters, to return maximum revenue to the public treasury. In theory, the tax rates should be set or raised to such a level that the air is “clean enough” and that polluters would find it more economical to control the emissions than pay the taxes. 4.5 COST-BENEFIT APPROACH This copy is issued to Lau Chin Tung In this strategy, the costs of all damages resulting from air pollutants and the costs of all control measures need to be quantified, and the pollution control option(s) which minimizes the sum of pollution damage and pollution control costs will be adopted. The assumption of this approach is that either there are no thresholds, or they are low enough that we cannot afford to have air that clean. Hence, we have to accept some amount of air pollution damage and the damage we should accept should correspond to how much we are willing to pay. 4.6 SOCIO-ECONOMIC AND POLITICAL ISSUES, POLLUTER PAYS PRINCIPLE In addition to be supported by scientific evidence, the AQM process needs to address the socio- economic and political issues as the attainment and maintenance of air quality depends also on public’s willingness to accept the costs of control, changes in lifestyle, additional legal requirements, and social and economic impacts. Compromises among various stakeholders may often be necessary and a typical example is the grandfathering practice of old emission sources. As a whole, it should be fair, transparent, consistent, cost-effective, evident based and consistent with principles including: a) The ‘polluter pays’ principle: Commonly accepted practice that those who produce pollution should bear the costs of managing it to prevent damage to human health or the environment. Accordingly, a factory that emits air pollutants is held responsible for controlling its emissions and rendering them harmless and inoffensive. b) Environmental equity principle: People with lower socioeconomic status are more likely more susceptible to air pollution because (i) they may be more frequently or more intensely exposed to air pollution; and (ii) they may have poorer health conditions and behaviour or traits (e.g., smoking, passive smoking, occupational exposure) that have synergic effects with urban air pollution. It is necessary to address concerns about inequitable burdens and benefits related to distributions of air pollution concentrations, exposure levels and associated health outcomes in formulating air quality management policies. As the feasibility and costs of achieving the air quality objectives are critical factors in the AQM decision making process, the conduct of a well-documented cost-benefit analysis to assess the total benefits and costs of various project or policy options is necessary to ensure the transparency of process and help address the socio-economic and political issues associated with the proposal. V.2024.05.10 Page 32 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 4.7 REGULATORY AND NON-REGULATORY APPROACHES The AQM strategy may be implemented by both regulatory and non-regulatory approaches. The former is simple, effective, and easy to implement and enforce. It is often associated with: a) Promulgation of specific emission limits b) Mandating the use of specific pollution control technologies c) Bans or restrictions on use of polluting materials or fuels d) Use of properly designed exhaust outlets (e.g., vents and chimneys) They may be imposed either by legislations or as licensing requirements. In Hong Kong, the main statutes on AQM include the Air Pollution Control Ordinance (APCO, Cap 311), Motor Vehicle Idling (Fixed Penalty) Ordinance (Cap 611), Ozone Layer Protection Ordinance (Cap 403), and their subsidiary legislations. Some statutory control requirements include: a) Stationary sources: Prohibit smoke darker than Ringelmann Shade 1 This copy is issued to Lau Chin Tung Require prior approval of installation of chimneys, boilers and furnaces Limit liquid fuel sulphur content to 0.005% Ban open burning Require non-road mobile machinery to comply with stringent emission limits Require construction work to operate according the stipulated control requirements to prevent dust emissions Licence control of specified process to require the use of BPM for preventing the emissions Impose stringent emission caps on power plants Require petrol filling stations to install vapour recovery systems Limit VOCs contents of paints, printing inks, consumer products adhesives, sealants and vehicle refinishing paints, fountain solutions and printing machine cleaning agents Require recovery of perchloroethylene from dry cleaning machines Ban asbestos import and requires approval/notification before commencement of asbestos abatement activities Ban CFC and other ozone depleting substances b) Vehicles: Adopt the stringent vehicle emission standards (e.g., Euro VI) for newly registered vehicles Ban idling vehicles Cancel registration of vehicles with excessive smoke or non-compliance with the emission standards Adopt tight fuel standards and limits sulphur content of vehicle diesel to 0.001% Ban leaded petrol Progressive phasing out of Euro IV diesel commercial vehicles c) Vessels: Limit local marine diesel sulphur content to 0.05% Require ocean going vessels to switch to 0.5% S diesel from 1 January 2019 A list of the APCO and its subsidiary legislations can be found in section 4.11. V.2024.05.10 Page 33 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR On the other hand, non-regulatory approach has the advantages of being flexible and able to augment the regulatory actions and accelerate the introduction of new control technologies. It can take the form of self-regulatory or voluntary programmes. The means used include: a) Requiring polluters to set specific environmental goals and voluntary reporting of non- compliance cases b) Promoting the polluters’ environmental awareness and encourage process changes c) Promoting better vehicle maintenance and eco-driving habits d) Public recognition of the participants e) Labelling of low emission products or facilities f) Provision of incentives (e.g., tax or fee reduction, one-off grant for installation of control equipment) In Hong Kong, many non-regulatory programmes have or are being implemented, including: a) The smoky vehicle reporting programme since 1999 b) The incentive programme to replace diesel taxis/light buses with LPG vehicles in 1999 c) The incentive programme to retrofit old diesel vehicles with particulate reduction devices in 1999 d) Subsidising LPG taxi owners to replace dysfunctional catalytic converters in 2014 This copy is issued to Lau Chin Tung e) Provision of ex-gratia payment to help phasing out of pre-Euro IV diesel commercial vehicles progressively by end 2019 f) Funding the franchised bus companies to retrofit Euro II and III franchised buses with selective catalytic reduction devices g) Subsidising the purchase of 6 double-deck hybrid buses and 36 single-deck electric buses for trial runs h) Promote electric vehicle adoption by first registration tax concession and subsidies under the One-for-One Replacement Scheme i) Funding schemes to promote green and innovative transport technologies j) Promoting trials for electric public transport and commercial vehicles k) The Fair Wind Charter signed by ship liners in 2011 to promote ocean-going vessels to switch to low S diesel oil while berthing In addition to the regulatory/non-regulatory control of emissions, roadside air quality in urban cities can also be improved by good transport management. Examples of transport management measures are: a) Designation of low emission zone to restrict the access and use of the roads within the zone by those vehicles with higher emissions b) Expansion of mass transit and rail network c) Rationalizing bus routes d) Encouraging walking and cycling e) Designation of car-free zone or pedestrian zone f) Utilization of intelligent transport systems g) Managing road space (e.g., through road pricing) Successful achievement and maintenance of air quality requires also that land-use, transportation, and environmental planning be closely interrelated with same common air quality goals clearly defined and vigorously pursued. V.2024.05.10 Page 34 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR To tackle regional air pollution, joint cooperation with other authorities is both necessary and essential. For example, the Hong Kong and Guangdong governments are working together to reduce the total amount of emissions and stop air quality from further deteriorating as soon as practicable, and in the long term to achieve good air quality for the whole region. A Pearl River Delta (PRD) Regional Air Quality Management Plan and regional emission reduction targets are established. To follow up on the tasks under the Management Plan, a Special Panel on PRD Air Quality Management and Monitoring has been set up under the Hong Kong-Guangdong Joint Working Group on Environmental Protection and Combating Climate Change (JWGEPCCC). 4.8 AIR QUALITY AND EMISSION LIMITS, AIR POLLUTANT NUISANCE, PREVENTION OF SIGNIFICANT DETERIORATION Air quality and emission limits The AQOs and emission limits usually include the following elements: a) Concentration limits (for both ambient and emissions; usually expressed as µg/m3 or mg/m3 and, This copy is issued to Lau Chin Tung for gaseous air pollutants, also in ppm, ppb, etc.) or emission limits (for emissions only; e.g., kg NOx/h, tonnes particulates/y, g SO2/kWh of electricity, g NOx/vehicle km) b) Averaging time: humans, animals, and plant tolerate less air pollution over longer periods; limits with a time period, e.g., 1-h, 24-h, 1-y, are appropriate c) Reference conditions: for fair and easy comparison, measurements should be corrected to specified reference temperature, pressure and other conditions d) Exceedance allowance: number of exceedances allowed in a given year or over multiple years, to account for the occasional odd weather condition or emission event e) Deadline for meeting the limits f) Consequence of not meeting the limits In the USA, primary and secondary air quality standards are set respectively for protection of human health and welfare based on sound science. The primary standards must be based on health protection with adequate margin of safety and preclude the use of costs. For air pollutants with no health thresholds, the decision will be based on the uncertainty that any given level is low enough to prevent health effects, and on the relative acceptability of various degrees of uncertainty. The secondary standards aim to protect welfare, e.g., soils, water, crops, animals, visibility, property, and personal comfort and well-being. These standards need to be re-evaluated periodically. Those locations fail to meet the standard will be designated as non-attainment areas (or “Air Quality Management Areas” in EU). Additional stringent measures will be required to be implemented to attain the standard within specific time frames. The WHO has also released in 2005 a set of air quality guidelines (AQGs) 18 for the common air pollutants. The guidelines aim to provide a uniform scientific basis for understanding the effects of air pollution on human health and development of the local AQOs. It also provides interim targets (ITs) for PM2.5/PM10, O3, SO2 as a guide to stage the necessary measures to improve the air quality. In 2021, the WHO has further tightened the guidelines for PM2.5, PM10, O3, NO2, SO2 and CO after a systematic review of the health effects from exposure to these air pollutants. 19 In Hong Kong, the AQOs are stipulated under the APCO to promote the conservation and best use of air in the public interest. The Authority shall aim to achieve the relevant AQOs as soon as is reasonably 18 World Health Organization, Air quality guidelines global update 2005 (https://www.who.int/publications/i/item/WHO- SDE-PHE-OEH-06.02) 19 World Health Organization, WHO global air quality guidelines. Particulate matter (PM 2.5 and PM10), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide, p.36-45, 2021 V.2024.05.10 Page 35 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR practicable and thereafter to maintain the quality so achieved. The first set of AQOs was established in 1987 and revised in 2014. The existing guiding principles established for AQOs are: a) Protection of public health b) Benchmarking against WHO guidelines c) Adoption of a staged approach for achieving ultimate WHO’s AQGs To fulfill the statutory requirement that AQOs are to be reviewed once every 5 years, the Secretary for Environmental Protection has revised the 24-h AQO of SO2 (from 125 to 50 µg/m3 (3 exceedances allowed each year)), the 24-h AQO of PM2.5 (from 75 µg/m3 (9 exceedances allowed each year) to 50 µg/m3 (35 exceedances allowed each year)) and annual AQO of PM2.5 (from 35 to 25 µg/m3). These new objectives have come into operation on 1 January 2022 and are shown in Table I-6. The AQOs are also used as: a) A benchmark for consideration of designated projects under the Environmental Impact Assessment Ordinance. b) A key factor to be considered when deciding whether a licence should be issued to a specified process under the APCO. This copy is issued to Lau Chin Tung Table I-6: Revised Hong Kong Air Quality Objectives (bold faced figures in the yellow highlighted boxes) WHO Interim Targets No. of Average WHO Air Pollutants IT-1 IT-2 IT-3 IT-4 Exceedances Time AQGs Allowed (Unit: µg/m3) Sulphur dioxide (SO2) 10-min 500 3 24-h 125 50 40 3 Nitrogen dioxide (NO2) 1-h 200 18 24-h 120 50 25 NA Annual 40 30 20 10 NA Carbon monoxide (CO) 1-h 30,000 0 8-h 10,000 0 24-h 7,000 4,000 0 Ozone (O3) 8-h 160 120 100 9 Peak 100 70 60 9 season* Respirable suspended 24-h 150 100 75 50 45 9 particulates (PM10) Annual 70 50 30 20 15 NA Fine suspended 24-h 75 50 37.5 25 15 35 particulates (PM2.5) Annual 35 25 15 10 5 NA Lead (Pb) Annual 0.5 NA * Average of daily maximum 8-h mean O3 concentration in the six consecutive months with the highest six-month running-average O3 concentration. V.2024.05.10 Page 36 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR Air pollutant nuisance Air pollution may also be a nuisance to the public. In the APCO of Hong Kong, nuisance caused by air pollution includes an event which is obnoxious and which, in the opinion of the Authority, results in one or more of the following: a) Dust deposition b) Objectionable odour c) Staining of, corrosion, or damage to, a building, plant, equipment, or other materials d) Eye, nose, skin irritation or other sensory discomfort e) Disturbance of normal activities by the colour or opacity of the emission f) Affect public safety g) Any other effect which is unreasonable for the public to suffer An air pollution abatement notice will be issued to the polluters causing or contributing to the nuisance to require cessation or reduction of the emission or taking any other steps to abate the emission with a specified period. Prevention of significant deterioration This copy is issued to Lau Chin Tung Prevention of significant deterioration (PSD) aims to: (i) preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreational, scenic, or historic value; and (ii) ensure that economic growth will occur in a manner consistent with the preservation of existing clean air resources. For these purposes, the USEPA has promulgated the PSD increments, i.e., the maximum allowable increase in concentration that is allowed to occur within the air quality standard ceiling, to prevent the air quality in clean areas in USA from deteriorating to the level set by its air quality standards. Significant deterioration of air quality will be assumed if the amount of new pollution exceeds the applicable PSD increment. 4.9 DISSEMINATION OF AIR QUALITY INFORMATION AND AIR QUALITY INDEX / AIR QUALITY HEALTH INDEX Maintaining an active communication is essential in air quality management as it helps prevent crises, conciliate interests, provide advance notice for the implementation of control measures, and inform the public the air quality situation and its associated risks. In Hong Kong, the air quality data are released on an hourly basis at EPD’s website. Among others, the air quality index, is a useful risk communication tool in translating technical air pollution data into information that the public can understand and use. It can help prevent acute exposures and symptoms by warning the public about high pollution levels and suggesting simple actions that can be taken to prevent exposure. The first system is USA’s Pollutant Standards Index (PSI). It was replaced by the Air Quality Index (AQI) in July 1999. The index varies from 0 to 500. AQIs less than 50 and 100 indicate respectively good and moderate air quality, whereas AQIs of 101 to 150, 151 to 200, 201 to 300, 301 to 500 are considered unhealthy for sensitive groups, unhealthy, very unhealthy, and hazardous, respectively. By comparing the concentrations of O3, particulates (PM10 and PM2.5), CO, SO2, and NO2 with their respective AQS, 5 sub-indices are produced. The highest sub- index is taken and reported as the AQI. V.2024.05.10 Page 37 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR The PSI and AQI systems suffer from several problems, including: a) Only the dominant air pollutant is used for calculating the index and hence the combined effect of air pollution is not taken into account b) The index may lag behind air pollution changes if the concerned air pollutant concentrations are of longer averaging time (e.g., 24-hr PM10 standard) c) The index may not reflect properly the related health impacts if the AQOs are established with the consideration of other factors To provide more useful and timely air pollution information to the public, Hong Kong launched an Air Quality Health Index (AQHI) 20 to replace its old Air Pollution Index system from 30 December 2013. AQHI informs the public the short-term health risk of air pollution and are calculated based on the total increased health risk attributable to the 3-hour moving average concentrations of O3, NO2, SO2 and particulates (PM2.5/PM10). The excess risk factors of each pollutant were obtained from local health studies. ⬚ Total increased health risk = 𝛽𝛽 𝑒𝑒 𝛽𝛽𝛽𝛽𝛽𝛽𝛽𝛽 − 1 This copy is issued to Lau Chin Tung where: Ci = concentration of the air pollutant (i.e., O3, NO2, SO2, PM2.5 or PM10) βi = excess risk factor of the air pollutant derived from Hong Kong’s local health data The AQHI is reported on a scale of 1 to 10 and 10+ and is grouped into five health risk categories (i.e., low, moderate, high, very high, and serious). The AQHIs are reported hourly at each ambient (“General AQHI”) and roadside (“Roadside AQHI”) station. To reflect the long-term health risk of air pollution, annual indices (i.e., 12-month moving averages divided by WHO’s 1-y AQGs), are released at EPD’s website. To alert the public before the onset of air pollution episodes, EPD also provides AQHI forecast. Relevant health advice is also provided to help the public, especially for susceptible groups such as children, elderly and those with heart or respiratory illnesses, to take precautionary measures (e.g., to reduce physical exertion when AQHI reaches “high” or above) to protect their health. 4.10 EDUCATION AND PUBLIC AWARENESS OF AIR POLLUTION Education on air pollution helps the public to be better aware of the importance of air pollution and the need for protecting the air environment. In Hong Kong, the EPD publishes in its website the “Clean Air Plan for Hong Kong 2035” and many other leaflets and resource materials to help the public better understand the air quality status and various air pollution management programmes. In launching new air quality management policy and programme, the public and relevant stakeholders will be engaged in the decision-making process. It helps the authority to have more complete information and make better and more easily implementable decisions that reflect public interests and values. In addition, it is a statutory requirement under the APCO of Hong Kong that the Advisory Council on the Environment will be consulted on the establishment of AQOs and other air quality management matters. 20 https://www.aqhi.gov.hk/en.html V.2024.05.10 Page 38 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 4.11 ORDINANCES AND SUBSIDIARY LEGISLATIONS ON AIR QUALITY MANAGEMENT The following is a list of major ordinances and their subsidiary legislations on air quality management in Hong Kong: 21 Air Pollution Control Ordinance (Cap 311) Air Pollution Control (Furnaces, Ovens and Chimneys) (Installation and Alteration) Regulations (Cap 311A) Air Pollution Control (Dust and Grit Emission) Regulations (Cap 311B) Air Pollution Control (Smoke) Regulations (Cap 311C) Air Pollution Control (Appeal Board) Regulations (Cap 311D) Air Pollution Control (Air Control Zones) (Declaration) (Consolidation) Order (Cap 311E) Air Pollution Control (Specified Processes) Regulations (Cap 311F) Air Pollution Control (Specified Processes) (Specification of Required Particulars and Information) Order 1993 (Cap 311G) Air Control Zones (Consolidation) Statement of Air Quality Objectives (Cap 311H) (Repealed) Air Pollution Control (Fuel Restriction) Regulations (Cap 311I) This copy is issued to Lau Chin Tung Air Pollution Control (Vehicle Design Standards) (Emission) Regulations (Cap 311J) Air Pollution Control (Specified Processes) (Removal of Exemption) Order 1993 (Cap 311K) Air Pollution Control (Motor Vehicle Fuel) Regulation (Cap 311L) Air Pollution Control (Specified Processes) (Removal of Exemption) Order 1994 (Cap 311M) Air Pollution Control (Specified Processes) (Specification of Required Particulars and Information) Order 1994 (Cap 311N) Air Pollution Control (Open Burning) Regulation (Cap 311O) Air Pollution Control (Asbestos) (Administration) Regulation (Cap 311P) Air Pollution Control (Specified Processes) (Removal of Exemption) Order 1996 (Cap 311Q) Air Pollution Control (Construction Dust) Regulation (Cap 311R) Air Pollution Control (Petrol Filling Stations)(Vapour Recovery) Regulation (Cap 311S) Air Pollution Control (Dry-cleaning Machines) (Vapour Recovery) Regulation (Cap 311T) Air Pollution Control (Emission Reduction Devices for Vehicles) Regulation (Cap 311U) Air Pollution Control (Volatile Organic Compounds) Regulation (Cap 311V) (Repealed) Air Pollution Control (Volatile Organic Compounds) Regulation (Cap 311W) Air Pollution Control (Air Pollutant Emission) (Controlled Vehicles) Regulation (Cap 311X) Air Pollution Control (Marine Light Diesel) Regulation (Cap 311Y) Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation (Cap 311Z) Air Pollution Control (Ocean Going Vessels) (Fuel at Berth) Regulation (Cap 311AA) (Repealed) Air Pollution Control (Fuel for Vessels) Regulation (Cap 311AB) Motor Vehicle Idling (Fixed Penalty) Ordinance (611) Motor Vehicle Idling (Fixed Penalty) Regulation (611A) Ozone Layer Protection Ordinance (Cap 403) Ozone Layer Protection (Fees) Regulations (Cap 403A) Ozone Layer Protection (Controlled Refrigerants) Regulation (Cap 403B) Ozone Layer Protection (Products Containing Scheduled Substances) (Import Banning) Regulation (Cap 403C) 21 https://www.elegislation.gov.hk/ V.2024.05.10 Page 39 Copyright @ 2024 Hong Kong Institute of Qualified Environmental Professionals Limited. All Rights Reserved.  I. AIR 5 AIR POLLUTION CONTROL TECHNOLOGY 5.1 CONTROL OF EMISSIONS FROM STATIONARY SOURCES Stationary sources may reduce their air pollution impacts by following, in the order of preference / effectiveness: 1. Prevent/reduce emissions, e.g., by: process/equipment changes fuel/raw material changes energy efficiency improvement and conservation 2. Control emissions, including proper operation and maintenance 3. Render emission inoffensive or harmless: e.g., by proper chimney dispersion (adequate chimney height and location, exit temperature, exit velocity Among others, electricity generation is a significant air pollution source in Hong Kong. To reduce its emissions, the following emission control measures have been imposed by the EPD and/or This copy is issued to Lau Chin Tung implemented by the two local power companies: