Chapter 14: Atmosphere

Atmosphere Definition: The atmosphere is a sphere of different gases around the earth. Components The component of the atmosphere may be divided into major, minor and trace components. The major components: (i) Major components of atmosphere are nitrogen (78.00%) and oxygen (21.01%). The minor components: (ii) Minor components of atmosphere are argon (0.93%) and carbon dioxide (0.04%). (iii) Trace components: The trace components are methane, hydrogen, neon, helium, krypton and xenon. Layers of atmosphere The atmosphere has four distinct layers which are determined by the change in temperature that is observed with increasing altitude. (i) Troposphere Definition: It is the lowest region of the atmosphere which extends up to 12 km. Temperature range: In this region, temperature decreases from 17°C to -58°C regularly. Characteristics • It includes all the major gases present in the atmosphere i.e., nitrogen, oxygen, and carbon-dioxide, etc. • It is the densest layer of the atmosphere. • It is the layer in which major events such as rain, lightening, and hurricanes occur (ii) Stratosphere Definition: Above the troposphere, the stratosphere lies which is at a distance of 12-50 km above the earth surface. Thermosphete Mesasphere 80-600 km 50-80 km Fig: Layers of the atmosphere Temperature range: Temperature increases from - 58°C to - 2°C. Divisions: Stratosphere can also be divided into three regions according to the distribution of ultraviolet radiations from the Sun. (a) Upper stratosphere: Since ozone in the upper layer absorbs high energy ultraviolet radiations from the Sun. It breaks down into monoatomic oxygen and diatomic oxygen. 3(g) (b) Middie stratosphere: The middle stratosphere has less ultraviolet radiations passing through it. Here, monoatomic oxygen and diatomic oxygen recombine to form ozone which is an exothermic reaction due to which formation of ozone layer takes place. 02(g) + 0° (c) Lower stratosphere: The lower stratosphere receives very low ultraviolet radiations, thus monoatomic oxygen is not found here and ozone is not formed here. (ili) Mesosphere Definition: It is third layer of atmosphere extends to a height of about 50 - 85 km from the ground. Temperature range: The temperature decreases with altitude from - 2°C to - 93°C. The coldest region of the atmosphere is located in this layer (iv) Thermosphere Definition: Above the mesosphere it extends from 85 km to 600 km above the earth surface. Temperature range: This is the region where the temperature increases as the altitude increases. The increase in the temperature is caused due to the absorption of energetic ultra- violet (UV) and X-rays. Temperature in the upper thermosphere can range from 500°C to 2000°C or higher. AIR POLLUTANTS

Air pollutants Definition: Pollutants are substances (gases, liquids and solids) that are harmful to the environment. Classification: Air pollutants can be classified as primary and secondary. Primary pollutants Definition: Primary pollutants are substances directly produced or emitted, such as ash from a volcanic eruption or carbon monoxide from a motor vehicle exhaust. Examples Oxides of carbon, Nitrogen and sulfur etc. Examples: The most important pollutants are mentioned below. (i) Oxides of Carbon (CO and CO2) (ii) Oxides of Nitrogen (NO and NO2) collectively known as NOx (iii) Oxides of Sulphur (SO2 and SO3) collectively known as SOx (3) 3(g) Secondary pollutants Definition: Secondary pollutants are formed due to chemical reactions of primary pollutants Examples PAN (peroxyacetyl nitrate), Sulfuric acid etc (IV) Hydrocarbons (Methane, Ethane) (v) Low altitude Ozone (O3) (V1) Chlorofluorocarbons (CFCs) (VIl) Polycyclic Aromatic Hydrocarbon (PAHs) (Vill) Persistent Organic Pollutant (POPs) (ix) Volatile Organic Compounds (VOCs) (x) Particulate Matter (PM) (xi) Heavy Metals (Pb, Hg and Cd) SOURCES OF AIR POLLUTION There are two main sources of air pollution. (i) Natural sources Naturally occurring particulate matter (PM) include dust from 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. • Thunderbolt produces significant quantities of oxides of nitrogen (NOx). • Other natural sources of air pollution are algae on the surface of the oceans, which gives out hydrogen sulfide (HS), wind erosion which introduces PM (particulate matter). Humid zones such as swamps, peat-bags or little deep lakes, which produce methane (CH4). (ii) Human-made sources These sources can be classified as mobile sources (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 produce carbon dioxide (COz) carbon-monoxide (CO), and hydrocarbons (CH4). • The burning of wood as a domestic fuel and coal in brick kilns are also the sources of air pollutants. Quick Check 14.1 (a) Mention important air pollutants: Ans. The most important pollutants are: (i) Oxides of Carbon (CO and CO2) (ii) Oxides of Nitrogen (NO and NO2) collectively known as NOx (iii) Oxides of Sulphur (SO2 and SO3) collectively known as SOx (iv) Hydrocarbons (Methane, Ethane) (v) Low altitude Ozone (O3) (vi) Chlorofluorocarbons (CFCs) (vii) Polycyclic Aromatic Hydrocarbons (PAHs) (viii) Persistent Organic Pollutants (POPs) (ix) Volatile Organic Compounds (VOCs) (x) Particulate Matter (PM) (xi) Heavy Metals (Pb, Hg and Cd) (b) Give the equations for the formation and depletion of ozone in the stratosphere. Ans. Formation of Ozone 03(8) - hr 0° (g) +02(g) (c) Write down the names and approximate height of different layers of atmosphere. Ans. The names and heights of different atmospheric layers are given below: Distance (Height above Layers the earth's surface) 0-12km Troposphere 12-50km Stratosphere 5.0-80km Mesosphere 80-600km Thermosphere SOURCES OF AIR POLLUTANTS Describe the oxide of carbon, nitrogen, sulfur, hydrocarbons and lower altitude ozone as air pollutants. Ans. Sources of air pollutants (i) Oxides of Carbon: The two oxides of carbon as air pollutants monoxide (CO) and carbon dioxide (CO2). 51* Carbon monoxide (CO): Carbon monoxide (CO) is produced mainly due to incomplete combustion of fossil fuels. 2C(s) + 02(g) 200(8) Do You Know? S.Q. Give effects of CO. Ans. Poisonous gas: Carbon monoxide is highly poisonous gas and cause suffocation if inhaled. It binds blood haemoglobin more strongly than oxygen thus excluding oxygen from normal respiration. The CO poisonous can be reversed by giving high pressure oxygen. Carbon dioxide (CO2) Carbon dioxide is the key greenhouse gas emitted by human activities like combustion of fossil fuels. Carbon dioxide (CO2) is a primary greenhouse gas that traps heat in the atmosphere, leading to global warming. C(s) +2(g) (ii) Oxides of Nitrogen (NOx) The gases like nitric oxide (NO) and nitrogen dioxide (NO2) are represented by NOx. Production: It is generally produced from burning fossil fuels NOx is produced as a result of the following chemical reactions: N2(g) +02(g) - in →20(8) (Nitric oxide) 2NO (8) +02(g) → 2NO 2(g) Natural sources: Natural sources of NO2 include microbial processes in soil and oceans where bacteria break down nitrogen compounds. › 0° (8) + 02(g) hV →03(g) Temperature Range 17 to -58°C -58 to -2°C -2 to -93°C 500 to 2000°C →CO 2(g) (Nitrogen-Dioxide) Artificial sources: Human activities include agricultural activities (synthetic fertilizers) and industrial processes (combustion of fossil fuels). Effects of NOx • It depletes the ozone layer • The increased levels of NO2 contribute to climate change and can also affect air quality. (iii) Oxides of Sulphur (SOx) There are two oxides of sulphur which are collectively called SOx which are named as: sulphur dioxide (SO2), sulphur trioxide (SO3). Sources: These gases are emitted primarily by burning coal and oil. Effects: When SOx combine water vapor, it causes acid rain that damages ecosystem. SO2 is the major source of acid deposition in the air. (iv) Hydrocarbons Natural sources: Hydrocarbons are produced naturally in various environmental processes like vegetation, wildfire, volcanoes, and seeps. Artificial sources: Anthropogenic 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. (v) Low-Altitude Ozone (O3) Oxidizing agent: Ozone is a powerful oxidizing agent. It is non-toxic in small concentrations, but above 100 parts per million (ppm), it is toxic. Effects: It is harmful to humans, plants and other materials i.e., rubber, fabric dyes, and durability and appearance of paints.

Sources of air Pollutants (i) Chlorofluorocarbons (CFCs) The decrease in the concentration of ozone in stratosphere is called depletion of ozone. This depleting of ozone has been caused by certain organic compounds called chlorofluorocarbons (CFCs). Sources: These compounds exist as gases or low boiling liquids at room temperature and are used as aerosols, as coolant in refrigerators and air conditioner Effects: Chlorofluorocarbons are known to diffuse into the stratosphere where they are broken down by UV radiation creating chloride free radical (Cl° .). The chloride free radical breaks down the Ozone molecule as: CFCe, -Ur ›CFCe, + Cl ClO+O →Cl. +0. The formation of another chlorine free radical in the last step that can further break down another molecule of O3. The 2nd and the 3rd steps are repeated many times. Interesting Information! S.Q. What are the main uses of CFCs in our daily life. Ans. Chlorofluorocarbons are used as propellants for refrigerators and air conditions. 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. Polycyclic Aromatic Hydrocarbon (PAHs) Polycyclic aromatic hydrocarbon (PAHs), composed of fused multiple aromatic rings are common environmental pollutants. Examples: The examples of PAHs are naphthalene, anthracene and phenanthrene. Sources: They are generated primarily during the incomplete combustion of fossil fuels (coal, oil, petrol, and wood), vehicle emissions, and industrial processes and even grilled foods. Some PAHs in the environment originate from the natural sources such as open burning, natural loss or seepage of petroleum and coal deposits. Effects: They have more potential of toxicity and carcinogenic properties. (ii) 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, traveled by wind and water. Sources: Most POPs are 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. Effects: POPs can have significant adverse effects on human health. Examples Table 14.1: Some POPs with their uses Names of POPs Polychlorinated Biphenyls (PCBs). Dichlorodiphenyl tri-chloroethane (DDT). (iii) Volatile Organic Compounds (VOCs) A large group of organic compounds that easily evaporates at room temperature are called VOCs. Sources: 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. Effects: • Exposure to VOCs can cause a variety of short term exposure effects irritation of eye nose, throat, headache and nausea. Long term exposure causes damage to the liver, kidney and central nervous system are long term exposures. • They are significant air pollutants contributing to indoor and outdoor air pollution. Examples: Some common VOCs are benzene, xylene, toluene, ethanol, formaldehyde and acetone. (iv) Particulate Matter (PM) Definition: 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 particulate matter (PM) comprises acids, organic chemicals, metals, and soil or dust particles. aerosols and as coolant in Uses Used in electrical equipment, surface. coating ink, adhesives and paints. Used as an insecticide in agriculture. Example: Particulate matter (PM) is all the dust, smoke, and haze particles suspended in ambient air Sources: Sources of PM are both natural and anthropogenic. • Natural sources include volcanoes, fires, dust storms, and aerosolized sea salt. • Man-made sources of particulate matter (PM) include combustion in mechanical and industrial processes, vehicle emissions, and tobacco smoke. (v) Heavy Metals (Lead, Mercury and Cadmium) Heavy metal like lead, mercury and cadmium can indeed be significant air pollutants. Sources: They are released into the atmosphere from various industrial processes, transportation and other human activities. Some major sources are metallurgy, battery waste and incineration. IMPACT OF HUMAN ACTIVITIES ON ATMOSPHERE

Human activities have significant impact on the atmosphere, primarily through the burning fossil fuels and deforestation. These activities contribute to climate change, air pollution, poor air quality and other environmental issues. Urban areas: Most air pollution comes from human-made sources in urban areas. Such sources can be classified as either mobile (cars, trucks, air planes, marine engines) or point sources (factories, electric power plants etc.) Impact of burning fossil fuels on the atmosphere Combustion of fossil fuels: The burning of fossil fuels is the primary cause of current climate change, altering the earth ecosystem and causing human and environment health problems. Effects: 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. Emitted Pollutants SO2 NH3 NO2 Fig: Impacts of air pollutants on the atmosphere Impacts of deforestation on the atmosphere Definition: Deforestation is purposeful cleaning or thinning of forests by humans. Deforestation represents one of the largest issues in global climate. Forests absorb Green House Gases (GHGs) like CO2 and clean air for us. Particles / aerosols 503* NO: Wet Deposition NH* Dry Deposition Effects of deforestation: Deforestation has a wide range of negative impact on the environment, including, loss of biodiversity climate change, soil degradation, and water cycle disruption. Quick Check 14.2 (a) Mention man-made sources of air pollution. Ans. Such sources can be classified as mobile sources (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 produce carbon dioxide (CO2) carbon-monoxide (CO), and hydrocarbons (CH4). The burning of wood as a domestic fuel and coal in brick kilns are also the sources of air pollutants. (b) How do polycyclic aromatic hydrocarbons (PAHs) primarily enter the atmosphere? Ans. They are generated primarily during the incomplete combustion of fossil fuels (coal, oil, petrol, and wood), vehicle emissions, and industrial processes and even grilled foods. Some PAH's in the environment originate from the natural sources such as open burning, natural loss or seepage of petroleum and coal deposits. (c) How do volatile organic compounds (VOCs) affect air quality? Ans. They contribute to the formation of smog, health problems and contribute to indoor as well as outdoor air pollution. (d) What are major sources of heavy metals in the atmosphere? Ans. Heavy metal like lead, mercury and cadmium can indeed be significant air pollutants. They are released into the atmosphere from various industrial process, transportation and other human activities. Major sources: Metallurgy, battery waste and incineration. EFFECTS OF AIR POLLUTION

Smog (It is the combination of two words that is smoke and fog.) Definition: Smog is a type of air pollution typically characterized by a thick haze. Causes: It primarily occurs in urban areas and is often caused by emissions from vehicle, industrial activities and other sources of pollution. Composition: It consists of fine dust or soot particles, condensed water vapor, poisonous gases like SO2, NOx, 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 Fig: Smog around Lahore fort (London Smog) (ii) Photochemical smog (Los Angeles Smog). i) Industrial or classical smog Industrial smog also called as "Reducing smog or Classical Smog" Source: It usually results from high quantities of sulfur oxides (SOx) being released into the air. It is also called London smog. (ii) Photochemical smog Photochemical smog is a type in which primary air pollutants like nitrogen oxides (NOx), VOC and unburned hydrocarbons undergo photochemical reactions in the Nitrogen oxides and volatile presence of sunlight and form orgar secondary pollutants like ozone and peroxyacetyl nitrates (PAN). Effects: This type of smog is considered more dangerous as it can cause heart palpitations, pneumonia and lung cancer Fig: Illustration of Photochemical smog ACID RAIN

Acid Rain Definition: When rain water has pH less than 5.6, it is known as acid rain it refers to precipitation (rain, snow sheet or hall). Mechanism: Burning of fossil fuels releases SOx and NOx into the atmosphere. These gases mix with the moisture in the air and form acids. Wind can carry these acidic droplets to huge distance. These droplets return to the ground as acid rain, acid hail, snow and even fog. Chemical reaction: The most important chemical reactions are as: 2502(g) + 2(g) SO 3(8) + H2O (0) → H,SO A (29) SO2 from fossil fuels is oxidized to SO which. then reacts with water to form sulphuric acid 2NO (8) + 02(g) Nitrogen oxide reacts with water to produce nitric acid and nitrous acid. 3NO 2 (g) + H2O(e) - Appearance Acid rain looks, feels and tastes like clean rain. Effects • It is corrosive in nature and can cause widespread damage to the environment • It effects building, soil, paper and paints etc. • It effects groundwater by making soluble the heavy metal ions like mercury lead and cadmium. Sunlight Brown photochemical smog pounds → 2503(6) → 2NO 2(g) → 2HNO 3(29) + NO GREEN HOUSE EFFECT AND GLOBAL WARMING Green-house effect Definition: The progressive warming up of the earth's surface due to blanketing effect of greenhouse gases in the atmosphere is called the greenhouse effect. It is a global scale problem of air Energy released pollution. back into space Global warming 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. Mechanism of global warming Carbon dioxide and water vapor in the atmosphere transmit short wavelength solar radiations but reflect back the longer wavelength heat radiation coming from warmed surface of the earth. The greenhouse effect is a phenomenon which is based on the gases to absorb infrared radiations. The mechanism of global warming is as follows: • 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. Quick Check 14.3 (a) Differentiate classical and photochemical smog. Ans. Classical smog It iș caused when primary air pollutants like nitrogen oxides It is caused by high VOCs sulfur (NOx), quantities of oxide being released photochemical reactions in the presence of sunlight and form secondary pollutants like ozone and peroxyacetyl! nitrates in air. (PAN). It is oxidizing smog. It is reducing smog. called It is also called Los Angeles smog. It is also London smog (b) Name greenhouse gases (GHGs). How do these gases cause global warming? Ans. Green-house gases: Carbon dioxide, Methane, Nitrogen dioxide, SF6, Greenhouse gases cause global warming. Greenhouse gases (trap heat) NO, SF. CO, Sunlight Reflected sunlight Energy absorbed Fig: Mechanism of Global Warming Photochemical smog and undergo unburned hydrocarbons Carbon dioxide and water vapor in the atmosphere transmit short wavelength solar radiations but reflect back the longer wavelength heat radiation coming from warmed surface of the earth. The greenhouse effect is a phenomenon which is based on the gases to absorb infrared 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. (c) Write a balanced equation, including state symbols, showing the formation of sulfuric acid from atmospheric sulfur trioxide, (SO3). Ans. → 2503(0) 25026) +0 2(g) (d) How HNO3 is formed from NO in the atmosphere? Ans. N2 reacts with Oz in atmosphere due to lightning to form NO. NO further oxidizes to give NO2, which mix with water to give nitric acid. Nitrogen oxide reacts with water to produce nitric acid and nitrous acid. 3NO 2(g) + H, 0(0) → 2HNO 3(aq) + NO (a) AIR QUALITY

Definition: Air Quality mole (AQL) is a measure of the concentrations of pollutants present in the air at a particular location. Air quality is measured in terms of Air Quality Index (AQI). Parameters • When the air quality is good, the air is clear and contains only small amount of solid particles and chemical pollutants. • Poor air quality, which contain high level, is often hazy and dangerous to health and the environment. • An AQI value under 50 is considered good in quality. This means, it is safe for you to spend time outdoor without posing a risk to your health. An AQI over 300 is considered hazardous. High risk population: Children under 18, adult over 65, people with chronic heart, and lung diseases are under high-risk. Outdoor workers are at higher risk because of the prolonged exposure. 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 SOx and NOx. 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 Natural Events: Wild fires can release large amounts of smoke and PM into the (iii) atmosphere. Natural dust storms can significantly lower air quality. (iv) 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 Air Quality Index Levels of Health Concern (AQI) Values Good O to 50 Moderate 51 to 100 101 to 150 Unhealthy for Sensitive Groups 151 to 200 Unhealthy 201 to 300 Very Unhealthy Hazardous 301 to 500 AIR POLLUTION AND HEALTH RISK

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. Following are the pollutants which effects adversely to human health. (i) Particulate matter (PM) Particular matter (PM) consists of tiny particles suspended in the air, including dust, dirt, soot and smoke ranging from diameter of 2.5 micrometer to 10.0 micrometer. Effects: Inhalation of these particulate matter (PM) can cause inflammation and irritation of airways, leading to conditions such as asthma and bronchitis. (ii) Nitrogen dioxide (NOz) and Sulphur dioxide (SO2) Effects: The short-term exposures of NO2 and SO2 can irritate the respiratory system, while long-term exposure can increase the risk of respiratory infection, asthma and bronchitis. Air quality and health risk Air pollution poses significant health risks to humans. The potential health effects can be acute or chronic. Main health risks associated with air pollutions (i) Respiratory Diseases Pollutants involved: ozone, particular matters (PM) and nitrogen dioxide (NO2) Effects: Increase asthma symptoms and trigger asthma attack. Long term exposure may lead to chronic cough and respiratory infections like pneumonia. Color Green Yellow Orange Red Purple Maroon (ii) Cardio-Vascular Diseases Exposure to particular matters and other pollutants can increase the risk of heart attack by causing inflammation, blood vessel damage, high blood pressure and heart stroke. (iii) Cancer Prolonged exposure to certain air pollutants especially causes lung cancer, particulate matter (PM), carcinogenic compounds (benzene formation). (iv) Reproductive and Developmental Effects Exposure to air pollution may negatively impact reproductive health and fertility in both man and women. Premature birth and developmental problems in children may occur Quick Check 14.4 (a) Explain the impact of particulate matter (PM) on the air quality. Ans. Inhalation of these particulate matter (PM) can cause inflammation and irritation of airways, leading to conditions such as asthma and bronchitis. Prolonged exposure to certain air pollutants like PM especially causes lung cancer. (b) What is AQI? How does it measure air quality? Ans. Air quality index AQI is a measure of the concentrations of pollutants present in the air at a particular location. If AQI is low, it means the air quality is good and safe for health while greater numbers of AQI refers to deteriorated quality of air and is not safe for health. (c) What are different levels of AQI. Mention the safest and the most hazardous ranges of AQI. Ans. Levels of Health Air Quality Index (AQI) Concern Values Good O to 50 Moderate 5:1 to 100 101 to 150 Unhealthy for Sensitive Groups 151 to 200 Unhealthy 201 to 300 Very Unhealthy 301 to 500 Hazardous METHODS AND TECHNIQUES TO MEASURE AND MONITOR AIR QUALITY

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 Air Pollutants: Particulate matter (PM), nitrogen dioxides (NOz), sulphur dioxide (SO2), carbon monoxide (CO), ozone (03) and Volatile organic compounds (VOC's). Nephelometer: 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 Color Green Yellow Orange Red Purple Maroon nephelometer. This is an instrument used to monitor PM such as dust, smoke, mist and fumes. Working principle: Nephelometer, also known as photometer, detects particles by measuring the total amount of light they scatter. Direct measurement methods (i) Continuous Emission Monitoring System (CEMS) Continuous emission monitoring system (CEMS) can usually monitor gas like CO, O3, SO2, NO2, VOC's and PM at industrial sites. (ii) Air Quality Monitoring Stations (AQMs) Fixed monitoring stations are equipped with various sensors and analyzers to measure pollutant level in real time located in urban areas and industrial zones. (iii) Remote Sensing Techniques (RST) Satellites equipped with sensors can measure atmospheric pollutants over large areas, providing valuable data on regional and global air quality. EXPERIMENTS AND DATA COLLECTION TO TEST HYPOTHESIS ABOUT AIR QUALITY The design of experiments to test hypothesis about air quality involves careful planning, data collection and analysis. Following steps should be done about the 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 sites 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. The reliable instruments and methods to collect air quality data are used 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 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. STRATEGIES USED TO REDUCE AIR POLLUTION

Strategies used to reduce air pollution A variety of technologies is used to reduce air pollution and improve air quality. The following five types of technologies we can be used to control emission of air pollutants. (i) Catalytic convertor (CC) Oxides of nitrogen and other undesirable gases such as CO and various unburnt hydrocarbon are emitted by the vehicle engines. The most cars are equipped with catalytic convertors to convert the harmful pollutants to harmless substances. Pollutants controlled: Following pollutants are converted by catalytic converter CO is oxidized to CO2, NOx are reduced to N2 and unburnt hydrocarbon is converted to CO2 and H2O. (ii) Diesel Particulate Filter (DPF) Diesel particulate filter (DPF) is incorporated in modern diesel engines to reduce the emission of harmful particulate matter (PM) from the exhaust gases. Pollutants controlled: The primary function of diesel particulate filter 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. Pollutants controlled: Following pollutants are converted NOx reduced to N2, CO and hydrocarbons are oxidized to CO2 and water vapors. Catalysts used: Pollutants are converted into harmless derivatives using catalysts, such as TiO2 and Zeolites, etc. (iv) Scrubbers Scrubbers can be used to control wide range of pollutants controlled particulate matters, SO2, Hcl, NH3 and VOCs. Working: Scrubbers use liquids (e.g. H2O) to remove pollutants. NO2 CO Engine PM Oxidation Catalyst Fig: Selective catalytic reduction AWS AND REGULATIONS RELATED TO ATMOSPHERE

Laws and Regulations Common rules and regulations to control air pollution in Pakistan is given below: • Pakistan Environmental Protection Act (PEPA 1997) • Natural Environmental Quality Standard (NEQS) • Punjab Environmental Protection (Amendment) Act 2012 Measures to control air pollutions (i) Vehicle Emission Standard Enforcement of this standard is to reduce pollution from motor vehicles. The promotion of cleaner fuels such as compressed natural gas (CNG), liquid petroleum gas (LPG) and sticker regulation on fuel quality. (ii) Industrial Emission Control To reduce emission from industrial resources and the encouragement of industries to adopt cleaner production techniques and pollution control technologies. (iii) Public Awareness Campaigns Educating the public about the sources and effect of air pollution and ways to reduce personal contributions to air pollution also promote the use of public transport carpooling and non-motorized transport such as cycling and walking. Urea SCR Urea Dosing • NH3 Oxidate Catalyst System (iv) Urban Planning and Green Infrastructure Development of green belts and parks in urban areas to improve air quality. Implementation of urban planning measures to reduce traffic congestion and promote sustainable transport options. (v) Smog Control Measures Specific measures to control smog particularly during the winter months when air quality deteriorates significantly. Restrictions the burning of crop residues, which is a major contributes to smog and should use smog towers and other technologies to reduce particulates matter in the air. (vi) Prohibition of the use of open fire For the disposal of domestic and industrial waste. Using open fire to bulk domestic and industrial waste can produce dust, smoke and significant amount of air pollutants. This should be prohibited (vii) Use of Low-Sulphur Diesel Reduction of permissible level of sulphur in diesel. Through these regulations and measures, Pakistan aims to improve air quality and minimize the adverse effects of air pollutions on public health and the environment. ECONOMICAL, SOCIAL AND POLITICAL ISSUES Social, economic and political issues caused by air pollution Air pollution and bad air quality is responsible for huge economic costs, social and political issues. (i) Economic Issues Poor air quality can reduce worker productivity due to illness and absenteeism. Air pollution and air quality can damage crops reducing agricultural yield and increasing food prices. Air pollution leading to acid rain. (i) Social Issues Vulnerable populations, such as children, the elderly and low-income communities are chronic exposure to polluted air reduces the overall quality of life. Severe air pollution can force people to migrate leading to social displacement. (iii) Political Issues Air pollution is not confined to borders and effective management requires international corporation. Implementing air quality regulations requires strict governance. Addressing air pollution requires a multi-faceted approach, balancing socio-economic and technological considerations.