[1] There are many different types of air pollutants, such as gases (including ozone, nitrogen oxides, sulfur dioxide, carbon monoxide, ammonia, and methane), particulates (such as soot), lead[2] and biological molecules.

Examples include ash from a volcanic eruption, carbon monoxide gas from motor vehicle exhausts, and sulfur dioxide released from factories.

[67][68] Although the World Health Organization recognizes CO2 as a climate pollutant, it does not include the gas in its Air Quality Guidelines or set recommended targets for it.

[citation needed] Increased levels of fine particles in the air are linked to health hazards such as heart disease,[78] altered lung function and lung cancer;[79] a definitive link between fine particulate pollution and higher death rates in urban areas was established by the Harvard Six Cities study, published in 1993.

[85] O3 is largely produced by chemical reactions involving NOx gases (nitrogen oxides, especially from combustion) and volatile organic compounds in the presence of sunlight.

[105] Growing evidence that air pollution—even when experienced at very low levels—hurts human health, led the WHO to revise its guideline (from 10 μg/m3 to 5 μg/m3) for what it considers a safe level of exposure of particulate pollution, bringing most of the world—97.3 percent of the global population—into the unsafe zone.

Indoor contaminants that can cause pollution include asbestos, biologic agents, building materials, radon, tobacco smoke, and wood stoves, gas ranges, or other heating systems.

Controlled wood fires in cook stoves and fireplaces can add significant amounts of harmful smoke particulates into the air, inside and out.

[114] Carbon monoxide poisoning and fatalities are often caused by faulty vents and chimneys, or by the burning of charcoal indoors or in a confined space, such as a tent.

[142] There are estimated 4.5 million annual premature deaths worldwide due to pollutants released by high-emission power stations and vehicle exhausts.

[143] A study concluded that PM2.5 air pollution induced by the contemporary free trade and consumption by the 19 G20 nations causes two million premature deaths annually, suggesting that the average lifetime consumption of about ~28 people in these countries causes at least one premature death (average age ~67) while developing countries "cannot be expected" to implement or be able to implement countermeasures without external support or internationally coordinated efforts.

[164] Household air pollution, for instance from cooking with solid fuels, but also from radon in building material, has been associated with cervical, oral, and esophageal cancer.

A 2014 WHO worldwide survey on maternal and perinatal health found a statistically significant association between low birth weights (LBW) and increased levels of exposure to PM2.5.

Women in regions with greater than average PM2.5 levels had statistically significant higher odds of pregnancy resulting in a low-birth weight infant even when adjusted for country-related variables.

[170] Health effects of air pollution on children include asthma, pneumonia and lower respiratory tract infections and low birth weight.

PM2.5 was also associated with reduced verbal fluency (for instance, number of animals one can list in a minute) and worse executive functions (like attention and working memory).

"[189][190] Choosing an appropriate Concentration Response Function and Value of a Statistical Life can be difficult for researchers in low and middle income countries.

[citation needed] The United Kingdom suffered its worst air pollution event when the 4 December Great Smog of 1952 formed over London.

In most developed countries, land-use planning is an important part of social policy, ensuring that land is used efficiently for the benefit of the wider economy and population, as well as to protect the environment.

[202] Stringent environmental regulations, effective control technologies and shift towards the renewable source of energy also helping countries like China and India to reduce their sulfur dioxide pollution.

The United States Environmental Protection Agency has published a compilation of air pollutant emission factors for a wide range of industrial sources.

[243] In the United Kingodm air pollution campaigning currently involves a mixture of grassroots activism (by groups such as Mums for Lungs and individual campaigners such as Rosamund Kissi-Debrah[244]), public health awareness (through events such as Clean Air Day), legal work (advanced by activist lawyers such as ClientEarth), and more traditional campaigning (by environmental groups such as Greenpeace and Friends of the Earth, public health advocacy groups such as British Lung Foundation and Asthma UK, and organizations that raise health and safety issues, such as the British Safety Council).

[250] The World Health Organization's Global Air Quality Guidelines encourage improvements in a similar way to national standards, but are "recommendations" and "good practice" rather than mandatory targets that countries must achieve.

[255] It has the potential to improve urban air quality as participating cities "exchange information, learn from best practices and consequently mitigate carbon dioxide emissions independently from national government decisions".

Indigenous groups frequently lack the political and financial clout to influence policy decisions that impact their lands and means of subsistence or to lessen the effects of climate change.

To promote persistence and environmental justice, Indigenous viewpoints must be acknowledged and integrated into efforts to mitigate the effects of climate change and adapt to them.

This entails defending treaty rights, advancing Indigenous sovereignty and self-determination, and aiding Indigenous-led projects for sustainable development and environmental preservation.

[261] Blacks and Latinos generally face more pollution than Whites and Asians, and low-income communities bear a higher burden of risk than affluent ones.

[262] Residents in public housing, who are generally low-income and cannot move to healthier neighborhoods, are highly affected by nearby refineries and chemical plants.

[263] Air pollution is usually concentrated in densely populated metropolitan areas, especially in developing countries where cities are experiencing rapid growth and environmental regulations are relatively lax or nonexistent.