Atmosphere

The atmosphere is a sphere of different gases around the earth. Its components are divided into major, minor and trace components. Major: nitrogen (78.00%) and oxygen (21.01%). Minor: argon (0.93%) and carbon dioxide (0.04%). Trace: methane, hydrogen, neon, helium, krypton and xenon.

The atmosphere has four distinct layers, determined by the change in temperature with increasing altitude:

i) Troposphere — the lowest region, extending up to 12 km. It includes all the major gases (nitrogen, oxygen, carbon dioxide, etc.). Temperature decreases from 17 °C to −58 °C regularly. It is the densest layer, and the layer in which major events such as rain, lightning and hurricanes occur.

ii) Stratosphere — above the troposphere, at a distance of 12–50 km above the earth's surface. Temperature increases from −58 °C to −2 °C. It is divided into three regions according to the distribution of ultraviolet radiations from the Sun. In the upper layer, ozone absorbs high-energy ultraviolet radiations and breaks down into monoatomic oxygen and diatomic oxygen:

O_3(g) —^hν→ O_2(g) + O^•_(g)

The middle stratosphere has less ultraviolet radiation passing through it. Here, monoatomic oxygen and diatomic oxygen recombine to form ozone, which is an exothermic reaction, due to which the ozone layer forms:

O_2(g) + O^•_(g) → O_3(g)

The lower stratosphere receives very low ultraviolet radiations, so monoatomic oxygen is not found here and ozone is not formed here.

iii) Mesosphere — extends to about 50–80 km from the ground. Temperature decreases with altitude from −2 °C to −93 °C. The coldest region of the atmosphere is located in this layer.

iv) Thermosphere — extends from 80 km to 600 km above the earth's surface. Temperature increases as altitude increases, because of the absorption of energetic ultraviolet (UV) and X-rays. Temperature in the upper thermosphere can range from 500 °C to 2000 °C or higher.

Pollutants are substances (gases, liquids and solids) that are harmful to the environment. Air pollutants are classified as primary and secondary. Primary pollutants are substances directly produced or emitted, such as ash from a volcanic eruption or carbon monoxide gas from a motor vehicle exhaust. Secondary pollutants are formed due to chemical reactions of primary pollutants — ground-level ozone and photochemical smog are the classic examples (see sec 9).

The most important pollutants are: 1. Oxides of Carbon (CO and CO₂); 2. Oxides of Nitrogen (NO and NO₂), collectively known as NO_x; 3. Oxides of Sulphur (SO₂ and SO₃), collectively known as SO_x; 4. Hydrocarbons (Methane, Ethane); 5. Low-altitude Ozone (O₃); 6. Chlorofluorocarbons (CFCs); 7. Polycyclic Aromatic Hydrocarbons (PAHs); 8. Persistent Organic Pollutants (POPs); 9. Volatile Organic Compounds (VOCs); 10. Particulate Matter (PM); 11. Heavy Metals (Pb, Hg and Cd).

📌 Quick Check 14.1 (answered from this chapter): (a) The important air pollutants are the 11 listed above. (b) Ozone formation and depletion in the stratosphere: O₃ —^hν→ O₂ + O^• (breakdown by UV), and O₂ + O^• → O₃ (exothermic re-formation) — see sec 1. (c) The layers and their approximate heights are: troposphere 0–12 km, stratosphere 12–50 km, mesosphere 50–80 km, thermosphere 80–600 km.

There are broadly two main sources of air pollution.

14.3.1 Natural sources. Naturally occurring particulate matter (PM) includes dust from the earth's surface, and biological materials in the form of pollens, spores and animal debris. Volcanic eruptions can introduce very large quantities of gases and particulate matter (PM) into the atmosphere. Thunderbolts produce significant quantities of oxides of nitrogen (NO_x). Other natural sources are algae on the surface of the oceans, which gives out hydrogen sulphide (H₂S), wind erosion which introduces PM, and humid zones such as swamps, peat-bogs or little deep lakes, which produce methane (CH₄).

14.3.2 Human-made sources. Such sources can be classified as either mobile (cars, trucks, air planes, marine engines) or point sources (factories, electric power plants etc.). The combustion of fossil fuels (coal, fuel oils, and natural gas) in vehicle engines, factories and power plants produces carbon dioxide (CO₂), carbon monoxide (CO), and hydrocarbons (CH₄). The burning of wood as a domestic fuel and coal in brick kilns are also sources of air pollutants.

14.4.1 Oxides of carbon. There are two oxides of carbon: carbon monoxide (CO) and carbon dioxide (CO₂).

Carbon monoxide (CO) is produced mainly due to incomplete combustion of fossil fuels:

2C_(s) + O_2(g) → 2CO_(g)

📌 Did You Know? (book's side note): Carbon monoxide is a highly poisonous gas and causes suffocation if inhaled. It binds blood haemoglobin more strongly than oxygen, thus excluding oxygen from normal respiration. The CO poisoning can be reversed by giving high pressure oxygen.

Carbon dioxide (CO₂) is the key greenhouse gas emitted by human activities like combustion of fossil fuels. It is a primary greenhouse gas that traps heat in the atmosphere, leading to global warming:

C_(s) + O_2(g) → CO_2(g)

14.4.2 Oxides of nitrogen (NO_x). The gases nitric oxide (NO) and nitrogen dioxide (NO₂) are represented by NO_x. These are generally produced from burning fossil fuels. NO_x are produced as a result of the following chemical reactions:

N_2(g) + O_2(g) —^{high T}→ 2NO_(g) (Nitric oxide)

2NO_(g) + O_2(g) → 2NO_2(g) (Nitrogen dioxide)

Natural sources of NO_x include microbial processes in soil and oceans where bacteria break down nitrogen compounds. Human activities include agricultural activities (synthetic fertilizers) and industrial processes (combustion of fossil fuels). NO_x depletes the ozone layer. The increased levels of NO_x contribute to climate change and can also affect air quality.

14.4.3 Oxides of sulphur (SO_x). There are two oxides of sulphur: sulphur dioxide (SO₂) and sulphur trioxide (SO₃), which are collectively called SO_x. These gases are emitted primarily by burning coal and oil. When SO_x combine with water vapour, they cause acid rain that damages the ecosystem. SO₂ is the major source of acid deposition in the air.

14.4.4 Hydrocarbons. Hydrocarbons are produced naturally in various environmental processes like vegetation, wildfire, volcanoes, and seeps. Anthropogenic (human-caused) activities like incomplete burning of fossil fuels, oil spills, industrial and vehicular emissions are sources of hydrocarbons. Automobiles are the major source of hydrocarbon emission. Methane is the most common hydrocarbon and air pollutant.

14.4.5 Low-altitude ozone (O₃). Ozone is a powerful oxidizing agent. It is non-toxic in small concentrations, but above 100 parts per million (ppm), it is toxic. It is harmful to humans, plants and other materials, i.e. rubber, fabric dyes, and affects them adversely. Note the contrast: ozone high in the stratosphere protects us (sec 1), while ozone at low altitude is itself a pollutant.

14.4.6 Chlorofluorocarbons (CFCs). The decrease in the concentration of ozone in the stratosphere is called depletion of ozone. This depleting of ozone has been caused by certain organic compounds called chlorofluorocarbons (CFCs). These compounds exist as gases or low boiling liquids at room temperature and are used as aerosols or refrigerants. CFCs are known to diffuse into the stratosphere where they are broken down by UV radiation, creating a chlorine free radical (Cl^•) — the book writes "chloride free radical", which is read here as the chlorine radical. The chlorine free radical breaks down the ozone molecule as shown in the following reactions:

CFCl₃ —^UV→ CFCl₂ + Cl^•

Cl^• + O₃ → ClO^• + O₂

ClO^• + O → Cl^• + O₂

The formation of another chlorine free radical in the last step means it can further break down another molecule of O₃. The 2^nd and the 3^rd steps are repeated many times — one radical destroys many ozone molecules in a chain.

📌 Interesting Information (book's side note): Chlorofluorocarbons are used as propellants for aerosols and as coolant in refrigerators and air conditioners. CFCs are 100,000 times more effective than CO₂ at preventing heat from escaping from the earth's atmosphere. The decomposition of one molecule of CFCs can destroy up to 100,000 molecules of ozone.

14.4.7 Polycyclic aromatic hydrocarbons (PAHs). PAHs, composed of fused multiple aromatic rings, are common environmental pollutants. Naphthalene, anthracene and phenanthrene are examples of PAHs. They are generated primarily during the incomplete combustion of fossil fuels (coal, oil, petrol, and wood), vehicle emissions, industrial processes and even grilled foods. Some PAHs in the environment originate from natural sources such as open burning, natural loss or seepage of petroleum and coal deposits. Naphthalene, anthracene and phenanthrene are examples of PAHs. They have potential toxicity and carcinogenic properties.

14.4.8 Persistent organic pollutants (POPs). These are organic compounds that are resistant to degradation through chemical, biological and photolytic processes. These are toxic and adversely affect human health and the environment, and are traveled by wind and water. Most POPs generated in one country can affect people and wildlife far from where they are used and released. Owing to their persistence, they accumulate in the environment and can have significant adverse effects on human health. Some POPs are given in Table 14.1: Polychlorinated Biphenyls (PCBs) — used in electrical equipment, surface coating ink, adhesives and paints; Dichlorodiphenyl tri-chloroethane (DDT) — used as an insecticide in agriculture.

14.4.9 Volatile organic compounds (VOCs). A large group of organic compounds that easily evaporate at room temperature. VOCs are emitted as gases from certain solids or liquids; liquid fuels are major sources of VOCs that impact outdoor air quality. Vehicle exhaust and burning liquid fossil fuels, wood and garbage all release VOCs into the atmosphere. Exposure to VOCs can cause a variety of health effects including eye, nose and throat irritation, headache, nausea after short term exposures, and damage to the liver, kidney and central nervous system after long term exposures. They are significant air pollutants contributing to indoor and outdoor air pollution. Some common VOCs are benzene, xylene, toluene, ethanol, formaldehyde and acetone, etc.

14.4.10 Particulate matter (PM). The term "particulate matter (PM)" refers to the wide variety of tiny substances that float in the air in the form of either solid particles or liquid droplets or both. PM is all the dust, smoke, and haze particles suspended in ambient air. PM comprises acids, organic chemicals, metals, and soil or dust particles. Sources of PM are both natural and anthropogenic. Natural sources include volcanoes, fires, dust storms, and aerosolized sea salt. Man-made sources of PM include combustion in mechanical and industrial processes, vehicle emissions, and tobacco smoke.

14.4.11 Heavy metals (Lead, Mercury and Cadmium). Heavy metals like lead, mercury and cadmium can indeed be significant air pollutants. They are released into the atmosphere from various industrial processes, transportation and other human activities. Metallurgy, battery waste and incineration are their major sources.

Human activities have significant impact on the atmosphere, primarily through the burning of fossil fuels and deforestation. These activities contribute to climate change, air pollution, poor air quality and other environmental issues. In urban areas, most air pollution comes from human-made sources. Such sources can be classified as either mobile (cars, trucks, air planes, marine engines) or point sources (factories, electric power plants etc.).

14.5.1 Impact of burning fossil fuels on the atmosphere. The burning of fossil fuels is the primary cause of current climate change, altering the earth ecosystem and causing human health problems. The burning of fossil fuels affects the earth system in a variety of ways. Some of these ways include greenhouse gas emission, air pollution and volatile organic compounds. (The book's Figure 14.2 shows emitted pollutants — SO₂, NO₂, NH₃, particles/aerosols — from power stations, motor vehicles and livestock, returning to land and water by dry and wet deposition.)

14.5.2 Impact of deforestation on the atmosphere. Deforestation represents one of the largest issues using global climate. Forests absorb GreenHouse Gases (GHGs) like CO₂ and clean air for us. In short, deforestation has a wide range of negative impacts on the environment, including loss of biodiversity, climate change, soil degradation, and water cycle disruption. (The book's wording "purposeful cleaning or thinning of forests by humans" is read as clearing/thinning of forests.)

📌 Quick Check 14.2 (answered from this chapter): (a) Man-made sources: mobile sources (cars, trucks, planes, marine engines) and point sources (factories, electric power plants), plus fossil-fuel combustion, wood fuel and brick kilns. (b) PAHs enter the atmosphere primarily from incomplete combustion of fossil fuels (coal, oil, petrol, wood), vehicle emissions, industrial processes and grilled foods, plus natural open burning and petroleum/coal seepage. (c) VOCs affect air quality as significant indoor and outdoor pollutants: they evaporate easily from fuels, exhaust, wood and garbage burning, and cause irritation/headache in the short term and liver, kidney and nervous-system damage in the long term. (d) Major sources of heavy metals: metallurgy, battery waste and incineration, plus industrial processes and transportation generally.

The most common effects of air pollutants are formation of smog and acid rain.

14.6.1 Formation of smog. Smog is a type of air pollution typically characterized by a thick haze. It primarily occurs in urban areas and is often caused by emissions from vehicle, industrial activities and other sources of pollution. It consists of fine dust or soot particles, condensed water vapor, poisonous gases like SO₂, NO₂, O₃, CO and CO₂, secondary pollutants like O₃, unburned hydrocarbons, VOCs and PM of size 10–2.5 micron.

Types of smog: i) Industrial or Classical Smog (London Smog); ii) Photochemical smog (Los Angeles Smog).

i) Industrial or classical smog. Also called "Reducing smog or Classical Smog". It usually results from high quantities of sulfur oxides (SO_x) being released into the air. It is also called London smog.

ii) Photochemical smog. A type in which primary air pollutants like nitrogen oxides (NO_x), VOC and unburned hydrocarbons undergo photochemical reactions in the presence of sunlight and form secondary pollutants like ozone and peroxyacetyl nitrates (PAN). This type of smog is considered more dangerous as it can cause heart palpitations, pneumonia and even lung cancer. (The book's Figure 14.4 labels the product "brown photochemical smog" — the brownish-yellow colour comes from nitrogen dioxide, NO₂, which is why the exercise asks about a yellow colour in photochemical smog.)

14.6.2 Acid rain. When rain water has pH less than 5.6, it is known as acid rain. It refers to precipitation (rain, snow or hail). Burning of fossil fuels releases SO_x and NO_x into the atmosphere. These gases mix with the moisture in the air and form acids. Wind can carry these acidic droplets to huge distances. Finally, these droplets return to the ground as acid rain, acid hail, snow and even fog. Acid rain looks, feels and tastes like clean rain. Its corrosive nature causes widespread damage to the environment. The most important chemical reactions are:

2SO_2(g) + O_2(g) → 2SO_3(g)

SO_3(g) + H₂O_(l) → H₂SO_4(aq)

SO₂ from fossil fuels is oxidized to SO₃, which then reacts with water to form sulphuric acid.

2NO_(g) + O_2(g) → 2NO_2(g)

Nitrogen oxide reacts with water to produce nitric acid and nitrous acid:

3NO_2(g) + H₂O_(l) → 2HNO_3(aq) + NO_(aq)

Global warming refers to the long-term rise in the Earth's average surface temperature due to human activities, primarily the emission of greenhouse gases (GHGs) released by burning fossil fuels. The progressive warming-up of the earth's surface due to the blanketing effect of greenhouse gases in the atmosphere is called the greenhouse effect. It is a global scale problem of air pollution.

Carbon dioxide and water vapour in the atmosphere transmit short wavelength solar radiations but reflect back the longer wavelength heat radiation coming from the warmed surface of the earth. The greenhouse effect is a phenomenon which is based on the ability of the gases to absorb infra-red radiations. In the day, heat from the sun (in the form of infrared) passes through the atmosphere heating up the earth. At night, the earth radiates heat to the outer space. Some atmospheric gases trap the heat from the sun, thus preventing the loss of heat. Higher the concentration of carbon dioxide gas and other gases, greater will be the absorption of thermal radiations and greater will be the increase of global temperature. The book's Figure 14.5 names CH₄, CO₂, SF₆ and NO_x as greenhouse gases trapping heat.

📌 Quick Check 14.3 (answered from this chapter): (a) Classical smog = reducing smog from high SO_x (London smog); photochemical smog = NO_x + VOCs + unburned hydrocarbons reacting in sunlight to form ozone and PAN (Los Angeles smog), more dangerous (heart palpitations, pneumonia, lung cancer). (b) Greenhouse gases (GHGs): CO₂, CH₄, water vapour, SF₆, NO_x (book's figure) — they transmit short-wave solar radiation but absorb/reflect back long-wave infrared heat from the warmed earth, so heat is trapped and the surface warms progressively. (c) Balanced equation for sulphuric acid from atmospheric sulphur trioxide: SO_3(g) + H₂O_(l) → H₂SO_4(aq) (the full chain is 2SO₂ + O₂ → 2SO₃, then SO₃ + H₂O → H₂SO₄). (d) HNO₃ from NO in the atmosphere: 2NO + O₂ → 2NO₂, then 3NO₂ + H₂O → 2HNO₃ + NO.

14.8 Air quality. Air quality is measured in terms of Air Quality Index (AQI). AQI is a measure of the concentrations of pollutants present in the air at a particular location. When the air quality is good, the air is clear and contains only a small amount of solid particles and chemical pollutants. Poor air quality, which contains a high level, is often hazy and dangerous to health and the environment. Air having an AQI value under 50 is considered good in quality — it is safe for you to spend time outdoor without posing a risk to your health. An AQI over 300 is considered hazardous. Children under 18, adults over 65, and people with chronic heart and lung diseases are under high-risk. Outdoor workers are at higher risk because of prolonged exposure.

14.8.1 Factors affecting air quality. Air quality is influenced by several key factors or sources. i) Emission sources: burning of wood and fossil fuels can increase local pollution level. Factories and power plants use fossil fuels that release dangerous pollutants in air like SO_x and NO_x. Vehicles release CO, PM and VOCs. ii) Meteorological conditions: wind, temperature, and humidity affect pollutant dispersion and concentration. A layer of warm air trapping pollutants near the ground can lead to poor air quality. Note on the book's numbering: the book jumps from (ii) straight to (iv) — no (iii) factor is printed; nothing has been invented to fill it. iv) Natural events: wild fires can release large amounts of smoke and PM into the atmosphere. Natural dust storms can significantly lower air quality. v) Seasonal changes: temperature variations, such as heating or cooling of buildings in different seasons, can increase emissions of pollutants. Seasonal pollen concentration can contribute to poor air quality.

Table 14.2 — AQI and level of health concern: 0 to 50 — Good — Green; 51 to 100 — Moderate — Yellow; 101 to 150 — Unhealthy for Sensitive Groups — Orange; 151 to 200 — Unhealthy — Red; 201 to 300 — Very Unhealthy — Purple; 301 to 500 — Hazardous — Maroon.

14.9 Air quality and human health. The link between air quality and human health is well-documented and significant. Poor air quality can have immediate and long-term health impacts.

14.9.1 Major air pollutants and their health effects. i) Particulate matter (PM): PM consists of tiny particles suspended in the air, including dust, dirt, soot and smoke ranging from diameter 2.5 micrometer to 10.0 micrometer (the book's stated range). Inhalation of these PM can cause inflammation and irritation of airways, leading to conditions such as asthma and bronchitis. ii) Nitrogen dioxide (NO₂) and sulphur dioxide (SO₂): short-term exposures to NO₂ and SO₂ can irritate the respiratory system, while long-term exposure can increase the risk of respiratory infection, asthma and bronchitis.

14.10 Air pollution and health risk. Air pollution poses significant health risks to humans. The potential health effects can be acute or chronic and vary depending on the type and concentration of pollutants, duration of exposure and individual weakness.

14.10.1 Main health risks associated with air pollution. i) Respiratory diseases: air pollutants such as ozone, particulate matter (PM) and nitrogen dioxide (NO₂) can increase asthma symptoms and trigger asthma attacks. Long term exposure may lead to chronic cough and respiratory infections like pneumonia. ii) Cardiovascular diseases: exposure to particulate matter and other pollutants can increase the risk of heart attack by causing inflammation, blood vessel damage, high blood pressure and finally heart stroke. iii) Cancer: prolonged exposure to certain air pollutants, especially particulate matter (PM) and carcinogenic compounds (benzene formation, in the book's words), causes lung cancer. iv) Reproductive and developmental effects: exposure to air pollution may negatively impact reproductive health and fertility in both men and women. Premature birth and developmental problems in children may occur.

📌 Quick Check 14.4 (answered from this chapter): (a) PM affects air quality as the suspended dust, smoke and haze particles in air — inhaled PM inflames and irritates the airways (asthma, bronchitis) and raises asthma symptoms; higher PM means poorer air quality. (b) AQI is the measure of pollutant concentrations in the air at a particular location: good air is clear with few solid/chemical pollutants; poor air is hazy with high pollutant levels and dangerous to health and the environment. (c) Levels of AQI (Table 14.2): Good 0–50 (Green) is the safest range; Hazardous 301–500 (Maroon) is the most hazardous range; in between: Moderate 51–100 (Yellow), Unhealthy for Sensitive Groups 101–150 (Orange), Unhealthy 151–200 (Red), Very Unhealthy 201–300 (Purple).

14.11 Methods & techniques to measure & monitor air quality. Measuring and monitoring air quality involves a combination of methods and techniques to assess the concentration of various pollutants in the air. These pollutants can include particulate matter (PM), nitrogen dioxides (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), and volatile organic compounds (VOCs). There are various methods and techniques used by environmental engineers to measure air quality accurately. The instrument used to measure air quality index (AQI) is the nephelometer. This instrument used to monitor PM such as dust, smoke, mist and fumes. Nephelometer, also known as photometer, detects particles by measuring the total light they scatter.

14.11.1 Direct measurement methods. i) Continuous emission monitoring system (CEMS): a continuous emission monitoring system can usually monitor gases like CO, O₃, SO₂, NO₂, VOCs and PM at industrial sites. ii) Air quality monitoring stations (AQMS): fixed monitoring stations are equipped with various sensors and analyzers to measure pollutant levels in real time, located in urban areas and industrial zones. iii) Remote sensing techniques: satellites equipped with sensors can measure atmospheric pollutants over large areas, providing valuable data on regional and global air quality.

14.12 Experiments and data collection to test hypotheses about air quality. The design of experiments to test hypotheses about air quality involves careful planning, data collection and analysis. The following steps should be done about air quality. i) Hypothesis: as a first step, a hypothesis is developed to design an experiment. For example, the hypothesis, "The concentration of airborne particulate matter (PM 2.5) and nitrogen dioxide (NO₂) in urban areas is higher during peak traffic hours as compared to non-peak hours" can be tested by collecting air quality data at different times of the day. ii) Designing the experiment: the detail of the experiment including the variables and method of data collection is planned. Busy roads and residential areas are selected for monitoring. iii) Data collection: the data on traffic volume during rush hours and non-rush hours is collected and finally compared. Reliable instruments and methods to collect air quality data are used.

14.13 Analyze data and interpret air quality. The collected data is analyzed to confirm the truth or falseness of the hypothesis. The results of the analysis are interpreted and concluded. Analyzing and interpreting air quality data involves measuring the contents of air pollutants and identifying trends over time. By carefully designing experiments, collecting and analyzing data, a hypothesis about air quality can be tested and the strategies for improving air quality can be made.

14.14 Strategies used to reduce air pollution. A variety of technologies is used to reduce air pollution and improve air quality. The following types of technologies can be used to control emission of air pollutants. i) Catalytic converter (CC): oxides of nitrogen and other undesirable gases such as CO and various unburnt hydrocarbons are emitted by vehicle engines. Most cars are equipped with catalytic converters to convert the harmful pollutants to harmless substances. CO is oxidized to CO₂, NO_x are reduced to N₂. The unburnt hydrocarbon is converted to CO₂ and H₂O. ii) Diesel particulate filter (DPF): DPF is incorporated in modern diesel engines to reduce the emission of harmful particulate matter (PM) from the exhaust gases. The primary function of DPF is to capture and store soot particles from the exhaust gases. iii) Selective catalytic reduction (SCR): SCR is used in diesel engines to remove pollutants from the emission gases. It reduces NO_x to N₂ and oxidizes CO and hydrocarbons to CO₂ and water vapour using catalysts, such as TiO₂, zeolites, etc. (The book's Figure 14.6 shows the SCR system with urea dosing, an oxidation catalyst and an NH₃ oxidation catalyst.) iv) Scrubbers: scrubbers can be used to control a wide range of pollutants including PM, SO₂, HCl, NH₃ and VOCs. Scrubbers use liquids (e.g. H₂O) to remove air pollutants.

14.15 Laws and regulations related to atmosphere. 14.15.1 Laws and regulations: rules and regulations to control air pollution in Pakistan are given below: i) Pakistan Environmental Protection Act (PEPA 1997); ii) National Environmental Quality Standard (NEQS); iii) Punjab Environmental Protection (Amendment) Act 2012.

14.15.2 Measures to control air pollution. i. Vehicle emission standard: enforcement of this standard is to reduce pollution caused by motor vehicles. The promotion of cleaner fuels such as compressed natural gas (CNG), liquid petroleum gas (LPG) and strict regulations on fuel quality is required. ii. Industrial emission control: to reduce emission from industrial resources, industries should be encouraged to adopt cleaner production techniques and pollution control technologies. iii. Public awareness campaigns: educating the public about the sources and effects of air pollution is a useful strategy, such as the use of public transport, carpooling and non-motorized transport such as cycling and walking. iv. Urban planning and green infrastructure: development of green belts and parks in urban areas to improve air quality and to reduce traffic congestion. v. Smog control measures: restriction of the burning of crop residues, and the use of smog control towers. vi. Prohibition of the use of open fire: using open fire to bulk domestic and industrial waste can produce dust, smoke and a significant amount of air pollutants. This should be prohibited.

14.16 Economic, social & political issues. Air pollution is responsible for huge economic costs, social and political issues. 14.16.1 Economic issues: poor air quality can reduce worker productivity due to illness. Air pollution and air quality can damage crops, reducing agricultural yield and increasing food prices. Air pollution may lead to acid rain. 14.16.2 Social issues: vulnerable populations, such as children, the elderly, and low-income communities, are at risk from chronic exposure to polluted air, which reduces the overall quality of life. Severe air pollution can force people to migrate, leading to social displacement. 14.16.3 Political issues: air pollution is not confined to borders and effective management requires international cooperation. Implementing air quality regulations requires strict governance. Addressing air pollution requires a multi-faceted approach, balancing socio-economic and technological considerations.