topic 8.3: urban air pollution

Pictureimage from www.igbp.net
Air pollution is the introduction of particulates, biological materials, or other harmful materials into the Earth's atmosphere, possibly causing disease, death to humans, damage to other living organisms such as food crops, or the natural or built environment.
It is estimated that more than 1 billion people are exposed to outdoor air pollution annually. Urban air pollution is linked to up to 1 million premature deaths and 1 million pre-native deaths each year. Urban air pollution is estimated to cost approximately 2% of GDP in developed countries and 5% in developing countries. Rapid urbanisation has resulted in increasing urban air pollution in major cities, especially in developing countries. Over 90% of air pollution in cities in these countries is attributed to vehicle emissions brought about by high number of older vehicles coupled with poor vehicle maintenance, inadequate infrastructure and low fuel quality.

In this unit we will look at the factors involved in the formation of urban air pollution and strategies to control air pollution.

​This unit is a minimum of 3 hours.
Guiding Questions:
  • How can urban air pollution be effectively managed?
  • What are the primary sources and consequences of urban air pollution on human health and the environment?
  • How do socioeconomic factors influence the distribution and severity of urban air pollution in different regions?
Understanding

air pollution

8.3.1 Urban air pollution is caused by inputs from human activities to atmospheric systems, including nitrogen oxides (NOx), sulfur dioxide, carbon monoxide and particulate matter.
  • ​Define particulate matter
  • Distinguish between PM2.5 and PM10 in terms of their sources and potential health impacts.
  • Explain how nitrogen oxides (NOx) contribute to urban air pollution and identify two major sources of NOx in urban environments.
  • Outline the primary human activities that contribute to the release of sulfur dioxide (SO2) in urban areas. Discuss one potential environmental impact of SO2.
Air pollution is a major global health threat, causing millions of premature deaths annually due to its links to strokes, cardiovascular diseases, lung cancer, and respiratory conditions. Despite efforts to enhance air quality, estimates from the World Health Organization (WHO) and the IHME’s Global Burden of Disease study attribute 7 million and 6.7 million deaths each year to both indoor and outdoor pollution from human-made and natural sources.
A study by Lelieveld et al. (2019) reveals that air pollution causes 8.8 million deaths annually, with 5.5 million from human activities like agriculture, residential energy use, and industrial emissions. Specifically, 3.6 million deaths are linked to fossil fuel combustion in power generation, transportation, and industry. The authors suggest that eliminating fossil fuels could prevent these deaths. The total impact of air pollution, including natural sources, reduces life expectancy by 26.5 years for those affected, with a global average loss of 2.9 years. The study focuses on particulate matter (PM2.5) and ground-level ozone.
​While many cities in North America and Europe have seen steady and relatively lower PM2.5 concentrations during the last few years, many cities (especially those in Asia) have been making strides in lowering their air pollution levels.

Nonetheless, many of them still record PM2.5 concentrations that are more than six times the WHO guideline.
Pictureimage from Energy Education
When fossil fuels are burned, two of the pollutants emitted are hydrocarbons (from unburned fuel) and nitrogen monoxide (nitric oxide, NO). Nitrogen monoxide reacts with oxygen to form nitrogen dioxide (NO2), a brown gas that contributes to urban haze. Nitrogen dioxide can also absorb sunlight and break up to release oxygen atoms that combine with oxygen in the air to form ozone.

Particulate matter is categorized according to size of particle, with PM2.5 being fine particulate matter with a diameter of 2.5 micrometres or less and PM10 being air pollution that is made of
larger particulate matter with a diameter of 10 micrometres.

Sources of Key Pollutants:
  • Nitrogen Oxides (NOx):
    • Emitted primarily from the combustion of fossil fuels in vehicles, power plants, and industrial facilities.
    • NOx plays a significant role in the formation of ground-level ozone and photochemical smog.
  • Sulfur Dioxide (SO2):
    • Produced mainly from the burning of coal and oil in power stations and industrial processes like metal smelting.
    • SO2 contributes to the formation of acid rain and respiratory problems.
  • Carbon Monoxide (CO):
    • Results from incomplete combustion of fossil fuels, commonly emitted by vehicles and industrial machinery.
    • CO is a colorless, odorless gas that can reduce oxygen delivery in the human body, leading to various health issues.

Particulate Matter (PM):
  • PM2.5:
    • Fine particles that penetrate deeply into the lungs and even enter the bloodstream.
    • Sources include combustion processes (e.g., vehicle engines, power plants), industrial activities, and secondary formation from gaseous pollutants.
  • PM10:
    • Larger particles that can cause respiratory issues but do not penetrate as deeply as PM2.5.
    • Sources include road dust, construction activities, and mechanical processes.

Health and Environmental Impacts:
  • PM2.5 and PM10:
    • PM2.5 is associated with severe health risks, including respiratory and cardiovascular diseases, as it can bypass the body's defense mechanisms and enter the bloodstream.
    • PM10 primarily affects the upper respiratory tract, causing issues like bronchitis and exacerbating asthma.
    • Both types of particulate matter contribute to reduced visibility (haze) and can have detrimental effects on ecosystems by depositing toxic substances onto soil and water bodies
Air Quality Standards
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Air quality standards set by the World Health Organization are not met in most regions worldwide, with low- and middle-income countries bearing the brunt of the impact. Addressing air pollution involves targeting key sources like transportation, energy production, and waste management, as well as encouraging cleaner household energy practices. These measures can greatly reduce pollution and its harmful health effects.
​8.3.2 Sources of primary pollutants are both natural and anthropogenic.
  • Define primary pollutants
  • Explain the difference between natural and anthropogenic sources of these pollutants.
  • Describe two natural sources of primary pollutants and the specific pollutants they release into the atmosphere.
  • Explain how the burning of fossil fuels for energy production contributes to the release of primary pollutants. Identify two specific pollutants that result from this process.
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Primary pollutants are substances that are emitted directly from a source and have an immediate impact on air quality. These pollutants are chemically active at the point of release and contribute directly to environmental degradation and human health problems.






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Natural Sources of Primary Pollutants:
  • Forest Fires:
    • Forest fires release significant quantities of particulate matter (PM), carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs) into the atmosphere. These emissions can travel long distances and affect air quality far from the source.
    • Example: The 2019-2020 Australian bushfires contributed to severe air pollution, affecting air quality across the region and even impacting other countries.
  • Dust Storms:
    • Dust storms occur when strong winds lift large quantities of dust and sand from arid or semi-arid regions, creating particulate matter that can degrade air quality.
    • Example: The Saharan dust storms, known as the "Saharan Air Layer," regularly affect air quality in the Caribbean and parts of North America.
  • Volcanic Eruptions:
    • Volcanic eruptions release large amounts of sulfur dioxide (SO2), ash, and particulate matter into the atmosphere. These pollutants can cause acid rain, reduce visibility, and have significant climate impacts.
    • Example: The 1991 eruption of Mount Pinatubo in the Philippines released vast quantities of SO2, contributing to global cooling effects.

Anthropogenic Sources of Primary Pollutants:
  • Agricultural and Forest Clearance Burning:
    • Burning biomass for land clearance in agriculture releases large amounts of carbon dioxide (CO2), carbon monoxide (CO), and particulate matter (PM). This practice is common in tropical regions where forests are cleared for farming.
    • Example: Slash-and-burn agriculture in the Amazon Rainforest contributes to air pollution and greenhouse gas emissions, significantly impacting regional air quality.
  • Fossil Fuel Combustion:
    • The burning of coal, oil, and natural gas for energy production in power plants, industrial facilities, and transportation is a major source of primary pollutants, including NOx, SO2, CO, and PM.
    • Example: Urban areas with high vehicular traffic, such as Los Angeles, experience elevated levels of NOx and PM, contributing to smog and poor air quality.
  • Biomass Burning for Energy:
    • In many parts of the world, particularly in developing countries, biomass (such as wood, crop waste, and animal dung) is burned for cooking and heating. This process releases CO, PM, and VOCs, leading to indoor and outdoor air pollution.
    • Example: In rural areas of India, the use of traditional biomass stoves is a significant source of household air pollution, leading to respiratory issues and other health problems.
  • Construction and Road Dust:
    • Construction activities and unpaved roads generate dust particles that contribute to PM pollution. These activities release large amounts of particulate matter, especially in rapidly urbanizing areas.
    • Example: In cities experiencing rapid growth, such as Beijing, construction dust contributes significantly to PM10 levels, affecting air quality and visibility.
Impact and Interaction of Natural and Anthropogenic Sources:
  • Natural and anthropogenic sources of primary pollutants often interact, exacerbating air quality issues. For instance, dust from construction sites can mix with emissions from vehicles, intensifying the concentration of particulate matter in urban areas.
  • Additionally, natural events like volcanic eruptions can worsen existing pollution levels by adding to the anthropogenic load of pollutants in the atmosphere.
Secondary Air Pollutants

Secondary air pollutants are produced in the air by the interaction of two or more primary pollutants or by reaction with normal atmospheric constituents, with or without photoactivation. Secondary pollutants are not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight; NO2, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.
Tropospheric ozone 
Pictureimage from apollo.eas.gatech.edu
Ozone occurs naturally at ground-level in low concentrations. The two major sources of natural ground-level ozone are hydrocarbons, which are released by plants and soil, and small amounts of stratospheric ozone, which occasionally migrate down to the earth's surface. Neither of these sources contributes enough ozone to be considered a threat to the health of humans or the environment.

Tropospheric ozone can act both as a direct greenhouse gas and as an indirect controller of greenhouse gas lifetimes. As a direct greenhouse gas, it is thought to have caused around one third of all the direct greenhouse gas induced warming seen since the industrial revolution.

The ozone that is a byproduct of certain human activities becomes a problem at ground level. With increasing populations, more automobiles, and more industry, there's more ozone in the lower atmosphere. Since 1900 the amount of ozone near the earth's surface has more than doubled. Unlike most other air pollutants, ozone is not directly emitted from any one source. Tropospheric ozone is formed by the interaction of sunlight, particularly ultraviolet light, with hydrocarbons and nitrogen oxides, which are emitted by automobiles, gasoline vapors, fossil fuel power plants, refineries, and certain other industries.
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image from Climate Change and Food Security
Application of skills: Plan an experiment to use an indicator species as a correlate for pollution in the local
environment.
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https://byjus.com/question-answer/lichens-are-used-as-pollution-indicators-because/
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https://studyandupdates.in/which-is-used-as-an-air-pollution-indicator/
8.3.3 Most common air pollutants in the urban environment are either derived directly or indirectly from combustion of fossil fuels.
  • Identify two primary air pollutants produced by the combustion of fossil fuels
  • Describe the sources and health impacts of particulate matter (PM2.5 and PM10) in urban environments.
Urban air pollution involves both direct and indirect pollutants. Direct pollutants are emitted directly from sources like vehicles and industrial processes, including nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), and particulate matter (PM). These pollutants have immediate effects on air quality and health.

Indirect pollutants are formed in the atmosphere through chemical reactions involving direct pollutants. For example, tropospheric ozone (O3) is produced when NOx and volatile organic compounds (VOCs) react with sunlight. Though not directly emitted, indirect pollutants can significantly impact health and the environment. These are commonly referred to secondary pollutants
​Summary Table for the Main Air Pollutants 
8.3.4 A range of different management and intervention strategies can be used to reduce urban air
pollution.
  • Describe two technological interventions used to reduce urban air pollution and explain how they work.
  • Explain how pedestrianized town centers can contribute to the reduction of urban air pollution.
  • Outline the role of green walls and natural screens in mitigating urban air pollution.
  • ​Identify and briefly explain the purpose of catalytic converters in reducing vehicle emissions
​Urban air pollution poses significant risks to human health and the environment. Effective management and intervention strategies are crucial for mitigating these risks and improving air quality in cities. These strategies range from technological interventions to urban planning and lifestyle changes.
Picturehttps://www.gov1.com/community-development/articles/pros-cons-making-public-transportation-free-Jz3LDt1L3yUKgv0o/
Improved Public Transportation:
  • Public Transit Expansion:
    • Expanding and improving public transportation systems, such as buses, trams, and trains, can significantly reduce the number of private vehicles on the road. This leads to lower emissions of primary pollutants like NOx, CO, and PM.
    • Example:​ The development of Bus Rapid Transit (BRT) systems in cities like Bogotá, Colombia, has reduced traffic congestion and air pollution by providing a reliable and efficient alternative to car travel.
  • Promotion of Electric Public Transit:
    • Transitioning to electric buses and trains can further reduce emissions from public transport, as these vehicles produce no tailpipe emissions.
    • Example: Shenzhen, China, has fully electrified its public bus fleet, leading to a significant decrease in urban air pollution
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Infrastructure for Cycling and Walking:
  • Bike Lanes and Cycling Infrastructure:
    • Developing dedicated bike lanes and cycling infrastructure encourages residents to use bicycles instead of cars, reducing vehicular emissions.
    • Example: Copenhagen, Denmark, is known for its extensive cycling infrastructure, which has contributed to its low levels of urban air pollution.
  • Pedestrianized Town Centres:
    • Creating pedestrian-only zones in city centers reduces car usage, leading to lower emissions and improved air quality. These areas also promote healthier lifestyles and can enhance urban livability.
    • Example: Many European cities, such as Vienna and Madrid, have pedestrianized their city centers, resulting in cleaner air and more vibrant public spaces.
Picturehttps://corticagarden.com/vertical-gardens-inspirations-for-green-walls/
Green Urban Planning:
  • Growing Trees and Urban Green Spaces:
    • Planting trees and creating green spaces in urban areas can help filter pollutants from the air, including PM, CO2, and NOx. Trees also provide shade, reduce urban heat islands, and improve overall environmental quality.
    • Example: New York City’s Million Trees Initiative aimed to plant a million trees across the city, enhancing air quality and providing numerous environmental benefits.
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  • Natural Screens and Green Walls:
    • Natural Screens: Rows of trees or shrubs planted alongside roads can act as natural barriers that trap pollutants and reduce their spread into residential areas.
    • Green Walls: Vegetated walls on buildings can absorb pollutants, reduce heat, and improve air quality in densely built urban environments.
    • Example: Green walls in cities like London have been implemented to reduce pollution levels near busy roads and enhance urban aesthetics.
Picturehttps://www.researchgate.net/figure/Schematic-image-of-a-three-way-automotive-catalytic-converter-HC-Hydrocarbons_fig1_337203725
Technological Interventions:
  • Compulsory Catalytic Converters:
    • Catalytic converters are devices fitted to vehicle exhaust systems that reduce harmful emissions, such as CO, NOx, and hydrocarbons. Making catalytic converters mandatory for all vehicles is a key strategy for reducing urban air pollution.
    • Example: The widespread use of catalytic converters in European countries has contributed to significant reductions in vehicle emissions over the past few decades.
  • Emission Control Technologies:
    • Technologies such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR) systems can be used in vehicles and industrial processes to further reduce emissions of harmful pollutants.
    • Example: Germany has implemented stringent emission standards that require the use of these technologies in both vehicles and industrial plants, leading to improved air quality.
Policy and Regulatory Measures:
  • Limited Car Use and Congestion Charges:
    • Implementing policies that limit car use, such as congestion charges, carpool lanes, or restrictions on driving in certain areas during peak pollution times, can reduce the number of vehicles on the road and lower emissions.
    • Example: London’s Congestion Charge Zone has effectively reduced traffic and air pollution in the city center by discouraging car use during peak hours.
  • Low Emission Zones (LEZs):
    • LEZs are areas where access is restricted to vehicles that meet specific emission standards, encouraging the use of cleaner vehicles and reducing pollution.
    • Example: Several European cities, including Berlin and Milan, have implemented LEZs to target high-emission vehicles and improve urban air quality.
Picture
https://viewpointvancouver.ca/2019/04/08/londons-new-ultra-low-emission-zone-reduces-pollution-sickness-deaths/
Public Awareness and Behavioral Change:
  • Education and Awareness Campaigns:
    • Raising public awareness about the sources and health impacts of air pollution can encourage behavioral changes, such as reducing car use, opting for cleaner transportation options, and supporting green initiatives.
    • Example: The “Smog Free Tower” project in the Netherlands, which combines technology with public art, has raised awareness about air pollution while also actively cleaning the air.
Case Studies:
Singapore’s Approach to Urban Air Quality:
  • Analyze how Singapore integrates a range of strategies, including green spaces, efficient public transportation, and strict vehicle emission standards, to manage urban air pollution.


Paris’s Efforts to Reduce Vehicle Emissions:
  • Evaluate Paris’s initiatives, such as the introduction of car-free days, electric vehicle incentives, and expanded bike-sharing programs, in reducing air pollution.

acid rain

​8.3.5 NOx and sulfur dioxide react with water and oxygen in the air to produce nitric and sulfuric acid, resulting in acid rain.
  • Describe the chemical reactions that lead to the formation of nitric acid (HNO3) from nitrogen oxides (NOx) in the atmosphere.
  • Explain how sulfur dioxide (SO2) contributes to the formation of sulfuric acid (H2SO4) and its role in acid rain.
  • Identify two environmental impacts of acid rain on ecosystems and infrastructure.
  • Outline the process by which NOx gases contribute to acid rain formation, including the relevant chemical equations.
​Acid rain refers to any form of precipitation (rain, snow, fog, or dust) that has been acidified by chemical reactions in the atmosphere. It is primarily caused by the release of sulfur dioxide (SO2) and nitrogen oxides (NOx) from human activities such as the burning of fossil fuels. These gases undergo chemical reactions in the atmosphere to form sulfuric acid (H2SO4) and nitric acid (HNO3), which then mix with atmospheric moisture and fall as acid rain.
Sources of NOx and SO2:
  • Nitrogen Oxides (NOx):
    • NOx gases, including nitric oxide (NO) and nitrogen dioxide (NO2), are produced during the high-temperature combustion of fossil fuels in vehicles, power plants, and industrial processes.
  • Sulfur Dioxide (SO2):
    • SO2 is mainly produced by the combustion of sulfur-containing fuels such as coal and oil in power plants and industrial facilities, as well as from natural sources like volcanic eruptions.
Chemical Reactions Leading to Acid Rain Formation:
  • Formation of Nitric Acid (HNO3):
    • Step 1: Oxidation of Nitric Oxide (NO) to Nitrogen Dioxide (NO2):
      • 2NO+O2→2NO2​
    • Step 2: Formation of Nitric Acid:
      • Nitrogen dioxide (NO2) further reacts with water (H2O) and oxygen (O2) in the atmosphere to form nitric acid (HNO3):
      • 4NO2+2H2O+O2→4HNO3​
    • Overall Reaction:
      • NOx reacts with water and oxygen to form nitric acid, which dissolves in water droplets and falls as acid rain.
Formation of Sulfuric Acid (H2SO4):
  • Step 1: Oxidation of Sulfur Dioxide (SO2) to Sulfur Trioxide (SO3):
    • 2SO2+O2→2SO3​
  • Step 2: Formation of Sulfuric Acid:
    • Sulfur trioxide (SO3) reacts with water (H2O) to form sulfuric acid (H2SO4):
    • SO3+H2O→H2SO4​
  • Overall Reaction:
    • SO2 reacts with oxygen and water to produce sulfuric acid, which is then incorporated into cloud droplets and precipitates as acid rain.
Picture
https://softbacktravel.com/what-is-acid-rain/
Transboundary Acid Deposition

Transboundary acid deposition occurs when sulfur dioxide (SO₂) and nitrogen oxides (NOx) from industrial sources travel across borders, forming acid rain. This leads to environmental damage, such as acidified lakes, degraded soils, and harmed ecosystems. The pollutants can affect areas far from their origin, making international cooperation essential for reducing emissions and mitigating impacts
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https://softbacktravel.com/what-is-acid-rain/
Case Study: Impacts of Acid Deposition Across Country Boundaries - The "Black Triangle" Region
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https://www.researchgate.net/figure/The-Black-Triangle-area-The-30-surface-stations-with-meteorological-observations-are_fig1_234308631
Picturehttps://www.researchgate.net/figure/The-Black-Triangle-area-The-30-surface-stations-with-meteorological-observations-are_fig1_234308631
​Background:
The "Black Triangle" region, where the borders of Germany, Poland, and the Czech Republic meet, is one of Europe's most notorious examples of transboundary acid deposition. This area has been heavily industrialized, with a dense concentration of coal-fired power plants, metal smelters, and factories, particularly during the mid-20th century. The region's name reflects the severe environmental degradation caused by high levels of sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions, which led to widespread acid rain.
Environmental Impacts:
  • Forest Damage: The Black Triangle experienced severe forest dieback due to acid rain, which leached essential nutrients like calcium and magnesium from the soil, while increasing the solubility of toxic metals such as aluminum. This resulted in widespread deforestation, particularly of coniferous trees, which are more susceptible to acidic conditions.
  • Water Acidification: Lakes and rivers in the region became highly acidic, leading to the loss of aquatic life, including fish and invertebrates. The acidification of water bodies also disrupted local fishing industries and contributed to the decline of biodiversity in aquatic ecosystems.
  • Soil Degradation: Acid deposition degraded soils, reducing agricultural productivity and harming local food supplies. The acidified soils also affected plant regeneration and forest recovery, further exacerbating environmental decline.
Cross-Border Impacts:
  • Transboundary Pollution: Air pollutants from the Black Triangle were carried by prevailing winds across national borders, affecting neighboring regions in Germany, Poland, and the Czech Republic. This led to international tensions, as the environmental damage extended beyond the immediate industrial zones.
  • Shared Environmental Degradation: Countries downwind from the Black Triangle, such as Germany, experienced acid rain impacts despite having stricter environmental regulations. This highlighted the need for cross-border cooperation to address transboundary pollution effectively.
Mitigation Efforts:
  • International Cooperation: In the 1990s, the governments of Germany, Poland, and the Czech Republic, with support from the European Union, initiated joint efforts to reduce sulfur dioxide and nitrogen oxide emissions in the Black Triangle. This included upgrading industrial facilities with flue gas desulfurization systems (scrubbers), transitioning to cleaner energy sources, and enforcing stricter environmental regulations.
  • Environmental Recovery: These efforts led to significant reductions in emissions and a gradual recovery of the region's forests, soils, and water bodies. However, the long-term impacts of acid deposition remain visible, and ongoing monitoring and remediation efforts are necessary.
8.3.6 Acid rain has impacts on ecology, humans and buildings.
  • Explain how acid rain affects the nutrient composition of soil in terrestrial habitats and discuss the consequences for plant growth.
  • Describe the impact of acid rain on freshwater habitats, focusing on the solubilization of aluminum and its effects on aquatic organisms.
  • Outline the process by which acid rain leads to the corrosion of marble and limestone structures.\
  • Identify two health impacts of nitrate and sulfate particles resulting from acid rain, and explain how these particles contribute to respiratory issues.
Acid rain has a number of negative impacts on ecosystems, humans and buildings.​​

Effects on Terrestrial Habitats:
  • Leaching of Nutrients:
    • Acid rain accelerates the leaching of essential nutrients such as calcium, magnesium, and potassium from the soil. This process depletes the nutrient availability for plants, leading to reduced soil fertility and negatively affecting plant growth and health.
    • Impact: Nutrient-deficient soils can lead to stunted growth in plants, weakened resistance to diseases, and reduced agricultural yields.
  • Toxification of the Soil:
    • The acidity from acid rain increases the solubility of toxic metals like aluminum, which can be released from soil particles into the soil solution. High levels of aluminum are toxic to plant roots, disrupting their ability to absorb water and nutrients. This is classified as an INDIRECT NUTRIENT EFFECT.
    • Impact: This toxification can lead to reduced biodiversity in terrestrial ecosystems as sensitive species are unable to survive in such altered soil conditions.
  • Direct Impact on Foliage:
    • Acid rain can directly damage the leaves and needles of trees and plants by dissolving the waxy protective coatings, leading to increased susceptibility to diseases, pests, and environmental stressors.
    • Impact: Visible damage includes leaf discoloration, reduced photosynthetic capacity, and premature leaf drop, which can weaken plants and trees over time. This is classified as a DIRECT EFFECT.
Picturehttps://www.e-education.psu.edu/egee102/h5p/embed/2231
Effects on Freshwater Habitats:
  • Toxicity Due to Aluminum Solubilization:
    • In acidified freshwater environments, aluminum solubilization from the soil can lead to toxic concentrations of aluminum in water bodies. This metal is highly toxic to aquatic organisms, particularly fish.
    • Impact: High aluminum levels can interfere with the ion balance in fish, leading to impaired gill function, difficulty in respiration, and, ultimately, fish mortality. Invertebrates and other aquatic organisms are also affected, leading to a decline in biodiversity.
  • Impacts on Fish Gills and Invertebrate Exoskeletons:
    • The acidic water conditions caused by acid rain can damage fish gills, reducing their ability to absorb oxygen. Invertebrates, such as crustaceans and insects, may experience weakened or deformed exoskeletons due to the acidity.
    • Impact: Acidic conditions can lead to population declines in fish and invertebrates, disrupting food chains and affecting the entire aquatic ecosystem. Sensitive species may disappear entirely, leading to a loss of biodiversity.
Picture
https://hess.copernicus.org/articles/24/4763/2020/
Picture https://chemistry1.quora.com/Why-does-acid-rain-damage-buildings
Effects on Buildings and Infrastructure:
  • Corrosion of Construction Materials:
    • Acid rain accelerates the corrosion of materials such as marble, limestone, steel, and paint. The acids in the rain react with these materials, leading to their gradual deterioration.
  • Marble and Limestone: These carbonate-based stones are particularly vulnerable. The acid rain reacts with the calcium carbonate (CaCO3) in the stone, forming calcium sulfate (CaSO4), which is more soluble and easily washed away by rainwater, leading to surface erosion.
  • Steel: Acid rain accelerates the rusting process in steel, weakening structural integrity over time.
  • Paint: Painted surfaces, particularly on buildings and vehicles, can peel, fade, or become damaged due to prolonged exposure to acid rain.
  • Impact: The corrosion of buildings, monuments, and infrastructure leads to increased maintenance costs, structural damage, and loss of cultural heritage, particularly in historic buildings and monuments.
​Effects on Human Health:

Physical acid rain itself is not harmful to humans. Thus, rain that comes into contact with your skin does not pose any health risks. However, all the gases that form this rain (nitrogen oxides, sulfur dioxide and sulfur trioxide), are harmful. If the small particles within the gas are inhaled, namely sulfate and nitrate, respiratory disease can occur.
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https://softbacktravel.com/what-is-acid-rain/
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  • Respiratory Issues from Nitrate and Sulfate Particles:
    • Acid rain contributes to the formation of fine particulate matter (PM2.5), which includes nitrate and sulfate particles. These particles can be inhaled deeply into the lungs, where they cause tissue damage and inflammation.
    • Tissue Damage and Lung Inflammation:
      • The inhalation of nitrate and sulfate particles can lead to respiratory conditions such as asthma, bronchitis, and other chronic lung diseases. These particles can also aggravate existing respiratory conditions, leading to increased hospital admissions and even premature death in vulnerable populations.
    • Impact: The presence of these particles in the air reduces overall air quality and poses a significant public health risk, particularly in areas with high levels of acid rain and industrial pollution.
8.3.7 Management and intervention strategies are used to reduce the impact of sulfur dioxide and NOx on ecosystems and to minimize their effects.
  • Explain how flue gas desulfurization (scrubbers) works to reduce sulfur dioxide emissions in power plants.
  • Describe two strategies that can be used to alter human activity in order to reduce emissions of NOx and SO2.
  • Outline the process of liming and discuss how it helps to restore ecosystems damaged by acid rain.
  • Identify and explain the role of catalytic converters in reducing NOx emissions from vehicles.
​​Sulfur dioxide (SO2) and nitrogen oxides (NOx) are major contributors to acid rain and other forms of air pollution, which have significant negative impacts on ecosystems, human health, and infrastructure. Effective management and intervention strategies are essential to mitigate these impacts. These strategies can be categorized into three main approaches: altering human activity, controlling pollutants at the point of release, and restoring damaged systems.
Altering Human Activity:
  • Alternative Energy Sources:
    • Renewable Energy:
      • Shifting from fossil fuels to renewable energy sources such as solar, wind, and hydroelectric power can significantly reduce SO2 and NOx emissions. These energy sources produce little to no emissions, helping to prevent the formation of acid rain and improving air quality.
      • Example: Denmark’s significant investment in wind energy has led to a substantial reduction in SO2 and NOx emissions, contributing to cleaner air and healthier ecosystems.
    • Energy Efficiency:
      • Improving energy efficiency in industrial processes, transportation, and residential energy use can reduce the overall demand for fossil fuels, thereby lowering SO2 and NOx emissions.
      • Example: Implementing energy-efficient technologies in manufacturing and construction can reduce the amount of fuel needed, leading to lower emissions.
  • Promoting Public Transportation and Electric Vehicles (EVs):
    • Encouraging the use of public transportation and electric vehicles reduces the number of fossil-fuel-powered vehicles on the road, decreasing NOx emissions from transportation.
    • Example: Cities like Oslo, Norway, have successfully promoted electric vehicles through incentives and infrastructure development, leading to reduced NOx pollution.
Picture
https://reneweconomy.com.au/wind-power-meets-and-beats-denmarks-total-electricity-demand-two-days-in-a-row/
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Wind power meets and beats Denmark’s total electricity demand – two days in a row
Controlling Pollutants at the Point of Release:
  • Flue Gas Desulfurization (Scrubbers):
    • How Scrubbers Work:
      • Flue gas desulfurization (FGD) systems, commonly known as scrubbers, are installed in power plants and industrial facilities to remove SO2 from exhaust gases before they are released into the atmosphere. These systems typically use a slurry of limestone (calcium carbonate) to react with SO2, forming gypsum (calcium sulfate), which can be removed and safely disposed of or used in construction materials.
      • Example: The widespread adoption of scrubbers in coal-fired power plants in the United States has significantly reduced SO2 emissions, helping to mitigate acid rain.
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https://www.saferack.com/glossary/air-scrubber/
  • Selective Catalytic Reduction (SCR) and Catalytic Converters:
    • SCR Technology:
      • Selective catalytic reduction (SCR) is a technology used in industrial plants and vehicles to reduce NOx emissions. It involves injecting a reductant, typically ammonia or urea, into the exhaust stream, which reacts with NOx in the presence of a catalyst to form harmless nitrogen (N2) and water (H2O).
      • Catalytic Converters in Vehicles:
        • Catalytic converters are devices fitted to vehicle exhaust systems that reduce emissions of NOx, CO, and hydrocarbons by catalyzing chemical reactions that convert these pollutants into less harmful substances.
      • Example: The implementation of catalytic converters in automobiles has greatly reduced NOx emissions in urban areas, contributing to improved air quality.
  • Low-NOx Burners:
    • How Low-NOx Burners Work:
      • Low-NOx burners are designed to minimize the formation of NOx during the combustion process in power plants and industrial facilities. They achieve this by controlling the temperature and oxygen levels during combustion, reducing the likelihood of NOx formation.
      • Example: The use of low-NOx burners in power plants across Europe has been a key strategy in reducing NOx emissions and mitigating their environmental impacts
Restoring Damaged Ecosystems:
  • Limestone Addition (Liming) to Lakes and Soils:
    • Purpose of Liming:
      • Liming involves adding limestone (calcium carbonate) to acidified lakes, rivers, and soils to neutralize acidity. This process helps to restore the pH balance, making the environment more suitable for aquatic life and plant growth.
      • Example: In Scandinavia, liming has been used extensively to combat the effects of acid rain on lakes, leading to the recovery of fish populations and improved water quality.
Picture
https://www.nordkalk.com/liming-acidified-lakes-and-watercourses-essential-for-a-balanced-future-environment/
  • Application of Fertilizers to Soils:
    • Purpose of Fertilization:
      • The application of fertilizers to acidified soils can help replenish essential nutrients that have been leached away by acid rain, improving soil fertility and promoting plant growth.
      • Example: In agricultural areas affected by acid rain, targeted fertilization has been used to restore crop yields and soil health.
  • Ecosystem Restoration and Reforestation:
    • Reforestation Efforts:
      • Planting trees and restoring forests in areas affected by acid rain can help stabilize soils, reduce erosion, and re-establish ecosystems. Trees can also act as natural buffers, absorbing CO2 and reducing overall greenhouse gas levels.
      • Example: Reforestation projects in regions affected by acid rain, such as the Appalachian Mountains in the U.S., have focused on restoring native tree species and improving forest health.
Public Health Interventions:
  • Healthcare Services:
    • Providing healthcare services and education in areas affected by high levels of SO2 and NOx can help manage the health impacts of these pollutants, such as respiratory diseases. Public awareness campaigns can also educate people about the risks of air pollution and encourage behaviors that reduce exposure.
    • Example: In heavily polluted urban areas, public health initiatives have focused on improving access to medical care for respiratory conditions and raising awareness about air quality issues.
Picture
image from www.tohoku-epco.co.jp

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8.3.8 Photochemical smog is formed when sunlight acts on primary pollutants causing their chemical transformation into secondary pollutants.
  • Explain the role of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the formation of photochemical smog. Include relevant chemical reactions in your explanation.
Picturehttps://energyeducation.ca/encyclopedia/Photochemical_smog
​Photochemical smog is a type of air pollution that results from the chemical reactions between primary pollutants and sunlight. This smog is most commonly observed in urban areas with high levels of vehicular and industrial emissions and is characterized by a brownish or yellowish haze in the atmosphere, particularly during warm, sunny days
.​Primary Pollutants Involved in Smog Formation:
  • Nitrogen Oxides (NOx):
    • NOx refers to a group of gases, primarily nitric oxide (NO) and nitrogen dioxide (NO2), which are released into the atmosphere through the combustion of fossil fuels in vehicles, power plants, and industrial processes.
    • Role in Smog Formation:
      • NOx gases play a critical role in the formation of photochemical smog as they are involved in the creation of tropospheric ozone (O3) and other secondary pollutants.
  • Volatile Organic Compounds (VOCs):
    • VOCs are a group of organic chemicals that easily evaporate into the atmosphere at room temperature. Common sources include vehicle emissions, industrial processes, gasoline vapors, and the use of solvents and paints.
    • Role in Smog Formation:
      • VOCs react with NOx in the presence of sunlight to produce secondary pollutants like peroxyacyl nitrates (PANs) and ozone, which are key components of photochemical smog.

Formation of Secondary Pollutants:
  • Tropospheric Ozone (O3):
    • Formation Process:
      • Tropospheric (ground-level) ozone is formed when NOx and VOCs undergo photochemical reactions in the presence of sunlight. ​
      • While stratospheric ozone protects us from harmful ultraviolet (UV) radiation, tropospheric ozone is a harmful pollutant that can cause respiratory problems, reduce crop yields, and damage ecosystems.
    • Impact of Tropospheric Ozone:
      • Tropospheric ozone is a major component of photochemical smog and is responsible for a variety of health problems, including irritation of the eyes, nose, and throat, and exacerbation of respiratory conditions like asthma.
  • Peroxyacyl Nitrates (PANs):
    • Formation Process:
      • PANs are formed from the reaction between NOx, VOCs, and oxygen in the presence of sunlight. They are highly reactive and toxic compounds that contribute to the overall harmful effects of photochemical smog.​
    • Impact of PANs:
      • PANs are particularly harmful to plants, causing damage to leaves, reducing photosynthesis, and inhibiting plant growth. They can also cause eye irritation and respiratory issues in humans.

​​Urban Areas with High Traffic and Industrial Activity:
  • Cities with dense traffic and numerous industrial facilities are more prone to photochemical smog due to the high emissions of NOx and VOCs.
Picture
https://energyeducation.ca/encyclopedia/Photochemical_smog
8.3.9 Meteorological and topographical factors can intensify processes that cause photochemical
smog formation.​
  • Describe the role of abundant sunlight (insolation) in the formation of photochemical smog. Why is smog more intense in areas with high levels of sunlight?
  • Discuss how reduced wind speed affects the concentration of pollutants and the formation of photochemical smog.
  • Outline the influence of topographical features, such as surrounding mountains, on the accumulation of photochemical smog in a city.
Picture
​Photochemical smog formation is significantly influenced by various meteorological and topographical factors. These factors can either promote or inhibit the accumulation of primary pollutants and their subsequent chemical transformation into secondary pollutants like ozone and peroxyacyl nitrates (PANs). Understanding these influences is crucial for predicting and managing smog episodes in urban areas.
​Meteorological Factors:
  • Abundant Insolation (Sunlight):
    • Role of Sunlight in Smog Formation:
      • Insolation refers to the amount of solar radiation reaching the Earth's surface. Abundant sunlight provides the energy required for the photochemical reactions that transform primary pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) into secondary pollutants like ozone (O3) and PANs.
    • Impact on Photochemical Smog:
      • Areas with high levels of sunlight, particularly during summer, are more prone to intense photochemical smog formation. The presence of strong UV radiation accelerates the photolysis of NO2, leading to increased ozone production.
    • Example: Cities in regions with hot, sunny climates, such as Los Angeles, California, and Mexico City, Mexico, often experience severe photochemical smog due to abundant insolation.
  
Picture
https://www.samaterials.com/content/photochemical-smog-automobile-exhaust.html

Reduced Wind Speed:
  • Wind and Pollutant Dispersion:
    • Wind plays a crucial role in dispersing pollutants. Reduced wind speed allows pollutants to accumulate near their sources, increasing the concentration of NOx and VOCs in the atmosphere.
  • Impact on Photochemical Smog:
    • When wind speeds are low, the stagnant air prevents the dispersion of pollutants, leading to higher concentrations of photochemical smog. This is particularly problematic in urban areas with dense traffic and industrial activity.
  • Example: On days with little to no wind, cities like Beijing, China, and New Delhi, India, can experience heightened smog levels due to the accumulation of pollutants.
Picture
https://link.springer.com/chapter/10.1007/978-981-16-7727-4_9
Temperature Inversion:
  • How Temperature Inversion Occurs:
    • Under normal atmospheric conditions, air temperature decreases with altitude, allowing warm air near the surface to rise and disperse pollutants. However, during a temperature inversion, a layer of warm air overlays cooler air at the surface, trapping the cooler air—and the pollutants it contains—near the ground.
    • Conditions Favoring Inversion:
      • Temperature inversions are more likely to occur during the night or early morning when the ground cools rapidly, particularly after a clear, calm day. They can also be exacerbated by high-pressure systems that suppress vertical air movement.
    • Impact on Photochemical Smog:
      • Temperature inversions trap pollutants close to the surface, preventing their dispersion and leading to the accumulation of smog. This can result in extremely poor air quality, particularly in the morning when inversion layers are most common.
    • Example: Precipitation cleans the air and winds disperse the smog. Thermal inversions trap the smogs in valleys (for example, Los Angeles, Santiago, Mexico City, Rio de Janeiro, São Paulo, Beijing) and concentrations of air pollutants can build to harmful and even lethal levels.  The infamous smog events in London, particularly the "Great Smog" of 1952, were worsened by temperature inversions that trapped pollutants close to the ground.
Picture
https://link.springer.com/chapter/10.1007/978-981-16-7727-4_9
Topographical Factors:
  • Surrounding Mountains:
    • Role of Mountains in Smog Formation:
      • Urban areas surrounded by mountains are more susceptible to photochemical smog because the mountains can act as barriers that trap air masses and prevent the horizontal dispersion of pollutants.
      • Impact on Photochemical Smog:
        • The trapped pollutants, combined with the effects of temperature inversions and abundant sunlight, can lead to severe smog episodes. The lack of natural ventilation in these areas exacerbates the concentration of pollutants.
      • Example: Mexico City, located in a basin surrounded by mountains, frequently experiences severe photochemical smog due to its topography, combined with high traffic and industrial emissions.
  • Urban Canyons and High Buildings:
    • Urban Canyons:
      • Urban canyons refer to streets flanked by tall buildings, which can create microclimates where air circulation is limited. These areas can trap pollutants, similar to how mountains do on a larger scale.
      • Impact on Photochemical Smog:
        • High-rise buildings can create localized temperature inversions within urban canyons, trapping heat and pollutants at street level. This can lead to the formation of smog "hot spots" where air quality is particularly poor.
      • Example: Cities with dense high-rise districts, such as New York City, USA, can experience localized smog formation in areas where tall buildings limit air movement.
Picture
https://link.springer.com/chapter/10.1007/978-981-16-7727-4_9
Interactions Between Meteorological and Topographical Factors:
  • Combined Effects:
    • The combination of meteorological and topographical factors can create ideal conditions for the formation and persistence of photochemical smog. For example, a city with a surrounding mountain range (topographical factor) and frequent temperature inversions (meteorological factor) will be particularly vulnerable to severe smog episodes.
    • Example: Los Angeles is a classic example of how both meteorological (abundant sunlight, temperature inversions) and topographical (mountain ranges) factors contribute to persistent photochemical smog problems.
Application of skills: Use graphs showing diurnal changes in urban air pollutants.
Use secondary databases to study change over time in local air quality, using a statistical tool to test the significance of any change
Diurnal Variation for Different Seasons
Picture
https://earthscience.stackexchange.com/questions/12048/how-to-explain-the-diurnal-variation-for-different-seasons
8.3.10 Direct impacts of tropospheric ozone are both biological and physical.
  • Explain how tropospheric ozone causes damage to plant cuticles and membranes, and discuss the potential consequences for agricultural productivity.
  • Describe the physical effects of tropospheric ozone on rubber materials and discuss the implications for industries that rely on rubber products.
  • Identify two ways in which tropospheric ozone affects materials, and suggest strategies to mitigate these effects.
Direct negative physical impacts of tropospheric ozone include degradation of natural fabrics, plastics and rubber. Direct negative biological impacts on human health and biodiversity
​
8.3.11 Indirect impacts of tropospheric ozone include societal costs and lost economic output.​
  • Outline the differential impacts of tropospheric ozone on poorer communities compared to wealthier ones.
  • Identify two ways in which economic inequality can be exacerbated by the indirect impacts of tropospheric ozone
While the direct biological and physical impacts of tropospheric ozone are well-documented, its indirect effects on society and the economy are equally significant. These impacts are often less visible but contribute to substantial societal costs, including increased healthcare expenses, reduced workforce productivity, and economic disparities, particularly affecting poorer communities.
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Poor air quality is one of the most serious environmental problems in urban areas around the world, especially in developing countries.  Adverse health effects from short and long term exposure to air pollution range from premature deaths caused by heart and lung disease to worsening of asthmatic conditions and can lead to reduced quality of life and increased costs of hospital admissions.

In Mexico City, such economic damages due to air pollution are estimated at $1.5 billion per year. In Jakarta, 14,000 deaths, about 2 per cent of annual deaths, in the cities could be avoided every year if particulate could be kept at the level recommended by the WHO. The researchers asserted that the health effects of air pollution are massive. It causes huge economic losses in terms of loss of current workforce, treatment cost, employment loss and so on. (New Age, January 1, 2004)

Air pollution also reduces food production and timber harvests, because high levels of pollution impair photosynthesis. In Germany, for example, about US$4.7 billion a year in agricultural production is lost to high levels of sulphur, nitrogen oxides, and ozone. 

The World Health Organisation estimates that about 700,000 deaths annually could be prevented in developing countries if three major atmospheric pollutants - carbon monoxide, suspended particulate matter, and lead - were brought down to safer levels. The direct health cost of urban air pollution in developing countries was estimated in 1995 at nearly US$100 billion a year. Chronic bronchitis along accounted for around US$40 billion).
Picture
image from South China Morning Post
Key Terms
Tropospheric Ozone (O3)
Primary Pollutants
Secondary Pollutants
Nitrogen Oxides (NOx)
Volatile Organic Compounds (VOCs)

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Tropospheric Ozone Formation
Temperature Inversion 
 Pollution Exposure
Workforce Productivity
Environmental Inequality
Low Emission Zones (LEZs)
Peroxyacyl Nitrates (PANs)
Acid Rain
Sulfur Dioxide (SO2)
Temperature Inversion
​Photochemical Smog
Flue Gas Desulfurization (Scrubbers)
Urban Planning
Renewable Energy Sources
​Particulate Matter
Catalytic Converters
​Classroom Materials
Subtopic 8.3 Urban Air Pollution Presentation.pptx
File Size: 22747 kb
File Type: pptx
Download File
Subtopic 8.3 Urban Air Pollution Workbook.docx
File Size: 1824 kb
File Type: docx
Download File

​
New Delhi Photochemical Smog Case Study activity 

Case Studies
On a Clear Day You Can See Forever 
New Delhi
China
Mexico City
​Asian Brown Haze

​Examples of the impacts of acid deposition on aquatic, terrestrial and human systems​
China
Canada and the Unites States
Sweden
​​​​​​Correct use of terminology is a key skill in ESS. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Useful Links

AirNav.gov - Check the air quality in various cities in the United StatesAir Pollution Interactive Map​
Smog City 2 
Photochemical Smog Formation - eHow
Animated map showing how Seattle’s urban air pollution migrates to the Mount Rainier 
Air pollutants.US Environmental Protection Agency’s site on air pollution and fossil fuels. - EPA
6 Common Air Pollutants - EPA
Clean Air Pollution Control Strategies - Clean Air World
Ways To Reduce Fossil Fuels - eHow
Catalytic Converter - Wikipedia
Ways to Reduce Air Pollution - EPA
Ways to Prevent Air Pollution - Buzzle
Clean Air Act - Wikipedia
Stockholm Convention -UNIDO
EPA animation outlining the formation and consequences of acid rain
Acid Rain Facts - National Geographic
Animation depicting the formation of acid rain and its consequences. From AbsorbLearning.com
Flash animation about acid rain from GoAnimate.com
Australian site for acid rain. - Asuetute
What is Acid Rain - EPA
Ocean Acidification - National Geographic
Liming Acid Lakes - Virginia Cooperative Extension
1979 Long Range Transboundry Air Pollution

In The News
America’s Air is Getting Cleaner and Less Costly - CNNMoney 24 April 2013
Here’s a paper on biological indicators of air pollution - National Academies Press
China's Tianjin To Restrict Vehicle Use To Curb Pollution - Yahoo News 19 May 2014
Urban pollution 2.5 times higher, health risks - EU Times 19 May 2014
Singapore braces for worst 'haze' as Indonesia fails to halt slash-and-burn clearances - Reuters 21 May 2014
Paris offers free public transport to reduce severe smog - BBC News 14 March 2014
Pollution Pandemic - Open Knowledge November 23, 2010
Pollution in China - The Guardian 18 July 2007
​Environmental Global Issues: Global Warming, Acid Rain, Depletion of Ozone Layer Effects - For The Future 13 Jan 2013
Schneiderman creates $400G Program to help reclaim acid rain-damaged waters of the Adirondacks - Environmental Headlines 23 Jan 2013
Organic carbon suggests Swedish lakes were less acidified - Physic.org Aug 01, 2011 Organic carbon suggests Swedish lakes were less acidified
International-mindedness:
  • The global rise of urbanization and industrialization has led to an increase in urban air pollution.
TOK
  • To what extent should scientific knowledge about the environmental and health impacts of fossil fuel combustion influence public policy and individual behavior?
Video Clips
Timelapse Coal Fired Power Plant from Jeff Grewe on Vimeo.
A segment on how air pollution affects urban populations. Produced by the Science & Medical Journalism Program at UNC-Chapel Hill.
Asia's dramatic economic growth in recent years has come with environmental costs that can take a heavy toll on people's health. While air pollution from busy factories and congested highways are part of the problem, there are also concerns about air quality in rural areas.
The air pollution in Mexico City is a serious problem that is shown in this short video.
As Beijing residents are told to limit time outside because of pollution, some of the 10 million residents in Shinjiazhuang, China's most polluted city, who are forced to wear masks every day, are starting to fight back
Air pollution is a global pandemic that's underway. It's a major health challenge yet nobody talks about it. It affects everyone but we usually ignore it cause we can't actually "see" it. Now it's time to talk about it and find a way to solve it together.
Learn the basics about Acid Rain. What causes acid rain?
​This groundbreaking NRDC documentary explores the startling phenomenon of ocean acidification, which may soon challenge marine life on a scale not seen for tens of millions of years
Clip from National Geographic's Appalachian Trail