Unit 14: Unit 14: Atmosphere — Long Questions

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.

(i) Major components: The major components of atmosphere are nitrogen (78.00%) and oxygen (21.01%).

(ii) Minor components: The 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.

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 monatomic oxygen and diatomic oxygen.
O₃₍ₑ₎ → O₂₍ₑ₎ + O•₍ₑ₎

(b) Middle stratosphere: The middle stratosphere has less ultraviolet radiations passing through it. Here, monatomic oxygen and diatomic oxygen recombine to form ozone which is an exothermic reaction due to which formation of ozone layer takes place.
O₂₍ₑ₎ + O•₍ₑ₎ → O₃₍ₑ₎

(c) Lower stratosphere: The lower stratosphere receives very low ultraviolet radiations, thus monatomic oxygen is not found here and ozone is not formed here.

(iii) 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 ultraviolet (UV) and X-rays. Temperature in the upper thermosphere can range from 500°C to 2000°C or higher.

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.

Secondary pollutants

Definition Secondary pollutants are formed due to chemical reactions of primary pollutants

Examples PAN (peroxyacetyl nitrate), Sulfuric acid 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
(iv) Hydrocarbons (Methane, Ethane)
(v) Low altitude Ozone (O₃)
(vi) Chlorofluorocarbons (CFCs)
(vii) Polycyclic Aromatic Hydrocarbons (PAHs)
(viii) 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 (H₂S), 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 (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.

Sources of air pollutants

(i) Oxides of Carbon: The two oxides of carbon as air pollutants monoxide (CO) and carbon dioxide (CO₂).

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

2C₍ₛ₎ + O₂₍ₑ₎ ⟶ 2CO₍ₑ₎

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₎ + O₂₍ₑ₎ ⟶ CO₂₍ₑ₎

(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₍ₑ₎ + O₂₍ₑ₎ ⟶ 2NO₍ₑ₎ (Nitric oxide)
high T

2NO₍ₑ₎ + O₂₍ₑ₎ ⟶ 2NO₂₍ₑ₎ (Nitrogen-Dioxide)

Natural sources Natural sources of NO₂ include microbial processes in soil and oceans where bacteria break down nitrogen compounds.

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 vapour, 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, volcanos, 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:

CFCl₃ ⟶ CFCl₂ + Cl•
UV

Cl• + O₃ ⟶ Cl• O + O₂

Cl•O + O ⟶ Cl• + O₂

The formation of another chlorine free radical in the last step that can further break down another ozone molecule of O₃. The 2ⁿᵈ and the 3ʳᵈ steps are repeated many times.

S.Q. What are the main uses of CFCs in our daily life.
Ans. Chlorofluorocarbons are used as propellants for aerosols and as coolant in 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 | Uses
Polychlorinated Biphenyls (PCBs). | Used in electrical equipment, surface coating ink, adhesives and paints.
Dichlorodiphenyl tri-chloroethane (DDT). | Used as an insecticide in agriculture.

(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.

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.

Human activities

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.

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.

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.

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 (London 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 (Los Angeles Smog).

Photochemical smog is a type in which primary air pollutants like nitrogen oxides (NOₓ), VOC and unburned hydrocarbons undergo photochemical reactions in the presence of sunlight and form 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.

Acid Rain

Definition When rain water has pH less than 5.6, it is known as acid rain it refers to precipitation (ram, snow sheet or hail).

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:

2SO₂₍ₑ₎ + O₂₍ₑ₎ ⟶ 2SO₃₍ₑ₎

SO₃₍ₑ₎ + H₂O₍ₗ₎ ⟶ H₂SO₄₍ₐq₎

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

2NO₍ₑ₎ + O₂₍ₑ₎ ⟶ 2NO₂₍ₑ₎

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

3NO₂₍ₑ₎ + H₂O₍ₗ₎ ⟶ 2HNO₃₍ₐq₎ + NO

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.

Note The answer for part (ii) Green-house effect continues beyond page 9 of the provided range.

Definition Air Quality mole (AQI) 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 SO₂ and NO₂. 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.

(iii) Natural Events: Wild fires can release large amounts of smoke and PM into the 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 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 (NO₂) 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.

(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

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 (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃) 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 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 tested and the strategies for improving air quality can be made.

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 convertor 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 vapours.

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.

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.

(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.

(ii) 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.