Greta Jimenez
Air pollution is a major threat to public health, the climate, and the environment. Urban areas are particularly vulnerable to poor air quality due to a combination of human activities and geographical features. The dense concentration of vehicles, industrial facilities, and construction projects are significant sources of emissions, contributing to the buildup of pollutants over cities. While air pollution has decreased over the past decades, it still affects almost 9 out of 10 people living in urban areas worldwide.
| Characteristics | Values |
|---|---|
| Primary sources of human-made air pollution | Vehicle emissions, fuel oils and natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical production |
| Natural sources of air pollution | Smoke from wildfires, ash and gases from volcanic eruptions, gases like methane emitted from decomposing organic matter in soils |
| Air pollutants | Nitrogen dioxide (NO2), ozone (O3), sulphur dioxide (SO2), methane (CH4), carbon monoxide (CO), volatile organic compounds (VOCs) and particulate matter (PM) |
| Air pollution and weather | Hot spells and poor air quality often occur together; wind can affect the flow of airborne pollutants; rain can "washout" particulate matter |
| Air pollution and health | Air pollution is associated with oxidative stress and inflammation in human cells, which may lay a foundation for chronic diseases and cancer; short-term exposure to higher levels of outdoor air pollution is associated with reduced lung function, asthma, cardiac problems |
| Air pollution and income | People with annual incomes above $70,000 experience greater declines in industry, energy, transportation, residential, and commercial-related emissions than people with lower incomes |
| Air pollution and urbanisation | Urban areas have poor air quality due to a combination of factors, primarily dense concentrations of vehicles, industrial facilities, and construction projects; high energy demands of cities lead to the combustion of fossil fuels |
| Air pollution interventions | Local interventions targeting pollution have improved air quality in some cities; for example, Beijing reduced its PM2.5 levels by 36% in 5 years through controls on power plant and industrial emissions, and new fuel quality and emission standards for vehicles |
What You'll Learn
Vehicle emissions
One of the main ways vehicles contribute to air pollution is through their exhaust fumes. The combustion of fuel in vehicle engines produces harmful by-products that are released into the air. This includes the formation of nitrogen oxides (NOx) through the burning of nitrogen in the air, which contributes to environmental issues such as acid rain and water quality deterioration. Diesel vehicles, in particular, are a major source of NOx emissions, accounting for 60% of transportation-related NOx emissions in the US.
Traffic congestion in urban areas exacerbates the problem by causing a build-up of pollutants in specific locations. Idling vehicles, particularly those near schools or busy roads, contribute significantly to air pollution as emissions are more concentrated at ground level. Additionally, the evaporation of fuel itself further adds to the overall emissions from vehicles.
While emission standards and regulations have helped reduce pollution levels over the years, more needs to be done. Encouraging the use of public transportation, electric vehicles, and alternative transportation options can help reduce vehicle emissions and improve air quality in cities.
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Industrial facilities
The widespread use of coal, and later oil-powered machinery, led to a sharp increase in carbon emissions and harmful environmental pollution. Industrial processes and power generation contribute to air pollution through the release of hazardous substances such as polycyclic aromatic hydrocarbons (PAHs) and nitrogen dioxide (NO2). PAHs are organic compounds containing carbon and hydrogen, which are produced as by-products of manufacturing and power generation, particularly in industries like iron, steel, and rubber product manufacturing. Nitrogen dioxide, mainly from vehicle emissions, is another significant pollutant in urban areas, linked to asthma development and aggravation in children.
In addition to air pollution, industrialization has also led to water pollution, with industrial chemicals and wastes contaminating water bodies. For example, the Cuyahoga River in Cleveland, Ohio, caught fire several times due to the presence of floating debris and oils. Industrial pollution has also degraded soil quality, with solid wastes from industries affecting agricultural lands. Furthermore, the release of heavy metals and other toxic substances by industries has harmed human health, plants, animals, and their habitats, altered breeding cycles, and damaged infrastructure.
While the environmental and health costs of European industry have decreased by a third from 2012 to 2021, industrial pollution remains a significant issue. In 2021, the costs of air pollution caused by Europe's largest industrial plants corresponded to about 2% of the EU's GDP, with just 1% of the most polluting facilities causing half of the total damage. These facilities, mainly coal power plants, continue to have severe environmental and health impacts, affecting not only the atmosphere and water ecosystems but also contributing to issues like microplastics in the ocean and the presence of pharmaceuticals in sewage.
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Construction projects
Another significant contributor to air pollution from construction sites is dust, which can be generated during land clearing, demolition, drilling, blasting, and other construction activities. This dust can remain in the air for extended periods, affecting nearby areas and the health of residents. Soil and gravel dust, in particular, can be easily blown off-site by wind or tracked off-site by vehicles, leading to air and soil pollution.
Construction activities also impact water systems, as runoffs from construction sites can carry pollutants, sediments, and chemicals into nearby water bodies, contaminating water sources and affecting aquatic life. Additionally, wastewater generated during construction, if not properly managed, can pollute local water bodies and alter the topography, impacting local ecosystems.
The extraction of raw materials, such as mining, quarrying, and logging, for construction projects can also lead to habitat destruction, water system pollution, and community displacement. Furthermore, the use of hazardous materials, such as toxic chemicals, paints, and treated woods, on construction sites contributes to air pollution and poses health risks to workers and nearby communities.
Noise and light pollution are also associated with construction work, disrupting sleep patterns, increasing stress levels, and affecting both human and animal health. The scale, duration, and specific activities of a construction project all influence the level of pollution generated, with larger-scale and long-duration projects having more significant impacts.
To mitigate the environmental and health impacts of construction projects, it is crucial to implement sustainable practices, such as using pollutant-free building materials, minimizing emissions, and adhering to environmental regulations. Real-time air quality monitoring and incentive systems for environmentally friendly practices can also help reduce the pollutants generated by construction projects.
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Fossil fuel combustion
One of the primary by-products of fossil fuel combustion is nitrogen oxides, which contribute to the formation of smog and acid rain. When excess nitrogen oxides are deposited back onto land, they can wash into nearby water bodies, causing pollution and harming aquatic life. Additionally, the release of nitrogen oxides into the atmosphere affects not only the air we breathe but also the quality of our land and water.
Furthermore, the dense concentration of vehicles in cities, many of which are powered by fossil fuels, exacerbates the problem. Vehicle emissions, particularly from diesel-fuelled cars, release harmful pollutants into the air, impacting the health of those who live and work in these areas. The high energy demands of cities further contribute to the combustion of fossil fuels, as they are still the primary source of energy for power generation.
The impact of fossil fuel combustion on the build-up of pollutants over cities is evident in the data. Many cities have seen persistently high levels of air pollution, with 41% of cities worldwide having air pollution levels over seven times higher than the World Health Organization's (WHO) recommendation. This has severe health consequences, particularly for children, who are more vulnerable to the adverse effects of toxic air pollutants and climate change.
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Natural sources
Wildfires, or forest fires, are a significant natural source of air pollution, releasing large quantities of particulate matter and other pollutants into the atmosphere. These fires can be caused by lightning strikes or natural burns and can have severe impacts on air quality, particularly in nearby cities.
Another natural source of pollution is wind-blown dust, which can pick up and transport pollutants over long distances, leading to haze and reduced visibility. Wind can also carry pollutants from other sources, such as power plants, over populated areas, exacerbating the issue of air pollution in cities.
In addition to these, volcanoes are also natural sources of pollution, emitting large amounts of ash, gases, and particulate matter into the atmosphere. While volcanic eruptions are less frequent than other natural sources, they can have significant and long-lasting impacts on air quality, particularly in nearby regions.
Agricultural activities also contribute to natural pollution sources. Farming practices, such as the use of manure and fertilizers, release gases like nitrous oxide (NOx) and methane (CH4) into the atmosphere. These gases contribute to air pollution and can have both local and global impacts.
Water bodies can also be affected by natural sources of pollution. Atmospheric deposition, a natural process, can distribute both natural and human-made contaminants into aquatic ecosystems through precipitation and other means. This can result in the widespread distribution of pollutants, impacting water quality and the health of aquatic life.
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Frequently asked questions
There are several factors that contribute to the build-up of pollutants over a city. Firstly, urban areas tend to have a dense concentration of vehicles, particularly those fuelled by diesel, which emit harmful pollutants such as nitrogen dioxide (NO2) and particulate matter (PM2.5). Secondly, industrial facilities and power plants burning fossil fuels, especially coal, release pollutants into the atmosphere, including sulphur dioxide and nitrogen oxides. Thirdly, construction projects and the combustion of solid fuels by residents for heating and cooking contribute to the problem. Finally, geographical features and weather conditions, such as wind patterns and street designs, can trap pollutants and prevent their dispersal, leading to a build-up of harmful substances.
Vehicles, especially those powered by diesel, are a significant source of air pollution in cities. Transportation accounts for about half of the emissions in urban areas. Vehicle emissions contain harmful pollutants such as nitrogen dioxide, particulate matter, and volatile organic compounds (VOCs). The dense concentration of vehicles in cities, coupled with congestion problems due to home deliveries and inadequate public transport infrastructure, exacerbates the pollution levels.
Industrial facilities and power plants burning fossil fuels, particularly coal, are major contributors to air pollution in cities. These facilities release pollutants such as nitrogen oxides, sulphur dioxide, and particulate matter into the atmosphere. In addition, industrial emissions and power plant controls have been shown to effectively reduce pollution levels, as seen in Beijing's successful implementation of emission standards.
Geographical features and weather conditions play a crucial role in the build-up of pollutants over a city. Tall buildings on either side of a street can create a "street canyon" effect, trapping pollution and restricting air flow. Climate change, which is influenced by human activities, is also a factor. Heatwaves and hot spells can worsen air quality by increasing the emission of natural volatile organic compounds (VOCs) from plants and enhancing photochemical reactions that produce ozone and secondary particulate matter.
