Urban Air pollution is the introduction of particulates, biological molecules, 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.
The atmosphere is a complex natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has been recognized as a threat to human health as well as to the Earth’s ecosystems.
Urban Air Pollution
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.
While most developed countries have put in measures to reduce vehicle emissions, in terms of fuel quality and vehicle emission reduction technologies, these measures are yet to be adopted in most cities in developing countries.

There are various locations, activities or factors which are responsible for releasing pollutants into the atmosphere of urban areas. These sources can be classified into two major categories.
Anthropogenic (man-made) sources:
These are mostly related to the burning of multiple types of fuel.
• Stationary sources include smoke stacks of power plants, manufacturing facilities (factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating devices. In developing and poor countries, traditional biomass burning is the major source of air pollutants; traditional biomass includes wood, crop waste and dung.
• Mobile sources include motor vehicles, marine vessels, and aircraft.
• Controlled burn practices in agriculture and forest management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the germination of some desirable forest trees, thus renewing the forest.
• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents
• Waste deposition in landfills, which generate methane. Methane is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement.
• Military resources, such as nuclear weapons, toxic gases, germ warfare and rocketry
Natural sources:
• Dust from natural sources, usually large areas of land with few or no vegetation
• Methane, emitted by the digestion of food by animals, for example cattle
• Radon gas from radioactive decay within the Earth’s crust. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.
• Smoke and carbon monoxide from wildfires
• Vegetation, in some regions, emits environmentally significant amounts of VOCs on warmer days. These VOCs react with primary anthropogenic pollutants—specifically, NOx, SO2, and anthropogenic organic carbon compounds — to produce a seasonal haze of secondary pollutants.
• Volcanic activity, which produces sulfur, chlorine, and ash particulate



Below are a few key consequences of urban air pollution.

Chemical reactions involving air pollutants can create acidic compounds which can cause harm to vegetation and buildings. Sometimes, when an air pollutant, such as sulfuric acid combines with the water droplets that make up clouds, the water droplets become acidic, forming acid rain. When acid rain falls over an area, it can kill trees and harm animals, fish, and other wildlife.

Acid rain destroys the leaves of plants.
When acid rain infiltrates into soils, it changes the chemistry of the soil making it unfit for many living things that rely on soil as a habitat or for nutrition. Acid rain also changes the chemistry of the lakes and streams that the rainwater flows into, harming fish and other aquatic life.
Rain can carry and deposit the Nitrogen in some pollutants on rivers and soils. This will adversely affect the nutrients in the soil and water bodies. This can result in algae growth in lakes and water bodies, and make conditions for other living organism harmful.
Ground-level ozone:
Chemical reactions involving air pollutants create a poisonous gas ozone (O3). Gas Ozone can affect people’s health and can damage vegetation types and some animal life too.
Particulate matter:
Air pollutants can be in the form of particulate matter which can be very harmful to our health. The level of effect usually depends on the length of time of exposure, as well the kind and concentration of chemicals and particles exposed to. Short-term effects include irritation to the eyes, nose and throat, and upper respiratory infections such as bronchitis and pneumonia. Others include headaches, nausea, and allergic reactions. Short-term air pollution can aggravate the medical conditions of individuals with asthma and emphysema. Long-term health effects can include chronic respiratory disease, lung cancer, heart disease, and even damage to the brain, nerves, liver, or kidneys. Continual exposure to air pollution affects the lungs of growing children and may aggravate or complicate medical conditions in the elderly.
some pollutants, if they are present in excessive quantities, can produce chemical and physical alterations of the air, hampering its capacity to “work” correctly and guarantee our survival functions. Men’s activity usually originates pollutants (anthropogenic origin), although in some cases natural sources contribute significantly. Most of human-origin urban air pollution derives either from fossil fuels (their combustion is necessary to produce energy) or from industrial chemical processes. The environmental impact of air pollutants is variable: some compounds mainly act at local level, where they are produced and distributed, while others affect entire regions.
Some others have an impact on the whole planet. In fact, some atmospheric agents have a short life (a few hours or a few days) and after that they fall on the ground, while other pollutants keep active for long periods and can spread on a wider area. This type of pollutants can have an influence on environmental conditions at a continental, sometimes even planetary level, with a negative impact on human health, even in places that are far away from the source of pollution. In most cases, the type and quantity of pollutants emitted into the atmosphere depend on the nature of the energy sources that are used (see the corresponding section on natural resources) and on the raw materials that men use during production processes.
The most basic solution for urban air pollution is to end its root causes: quit coal and move away from fossil fuels, replacing them with clean, renewable energy.
In the short-term, there are many intermediate solutions for urban air pollution. However, all of these solutions require governments to recognize the impact of urban air pollution on public health and the economy, and take action immediately.
• Make complete air quality information easily available to the public.
• Tighten the controls for power plant emissions to reduce emissions.
• Introducing cleaner fuel standards and switching to electric vehicles.
• Restrict the construction of power plants and other energy-intensive industries near residential areas.
• Improve urban planning to increase green spaces.
• Take air quality into consideration when conducting environmental assessments for major projects; for example, flyovers and highways should be far away from residential areas.

The solutions to urban air pollution are straightforward and simple but they require government action: quit coal, establish clear, strict air quality standards and introduce effective policy instruments to curb the rapid growth of the number of vehicles on the roads. Although the impact of big cities on local air quality has long been recognised, the impacts on regional and global climate are beginning to receive increased attention. We know now that air pollutants can drive climate change in complex ways (see Arneth et al. 2009, for example). Many pollutants (such as sulphur dioxide) form tiny droplets that deflect incoming solar radiation and tend to cool the climate. Pollution control policies that reduce the atmospheric concentrations of such substances can in fact lead to warming. Other pollutants – black carbon (soot) in particular – can absorb incoming solar radiation and lead to warming.

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2. “7 million premature deaths annually linked to air pollution”. WHO. 25 March 2014. Retrieved 25 March 2014.
3. Evidence growing of air pollution’s link to heart disease, death at the Wayback Machine (archived June 3, 2010) // American Heart Association. May 10, 2010
4. “Newly detected air pollutant mimics damaging effects of cigarette smoke” (PDF). Retrieved 2010-08-29.
5. “Infant Inhalation Of Ultra-fine Air Pollution Linked To Adult Lung Disease”. Sciencedaily.com. 2009-07-23. Retrieved 2010-08-29.
6. “The Effect of Changing Background Emissions on External Cost Estimates for Secondary Particulates”. Open environmental sciences. 2008.
7. David Pennise and Kirk Smith. “Biomass Pollution Basics”. WHO.
8. “Indoor air pollution and household energy”. WHO and UNEP. 2011.

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