Table 1.

Overview of ambient air pollutant sources and health effects. Data from Refs^{7, 19, 20, 27, 37, 39, 45, 55–57, 63, 64, 89, 96, 105, 130–133}

Key pollutants	Emission sources	Key health effects
Particulate matter (PM)	PM is a mixture of solid and/or liquid particles suspended in air They have both anthropogenic and natural sources and can be both directly emitted and formed in the atmosphere Human sources, include traffic, road dust, industrial sources (combustion of fossil fuels, metallurgy, ceramics, and others), domestic fuel combustion, and other human activities7 PM can form in the atmosphere as a result of chemical reactions of certain compounds like sulfur dioxide and nitrogen oxides Natural sources, including wildfires, soil dust, and sea salt	Associated with all-cause daily mortality and more highly associated with mortality from respiratory conditions19 Lowered life expectancy20 Asthma symptoms and exacerbation89 Coughing, wheezing, and breathlessness27,39 Impaired lung development in children45 and impaired lung function in adults55–57 Exacerbation of chronic obstructive pulmonary disease (COPD)96
Ozone (O3)	Not emitted directly, but formed as a product of chemical reactions between sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs) These primary or ‘precursor’ pollutants can be emitted from various sources, including traffic, power plants, refineries, chemical plants, and other sources130	Emphysema and decreased forced expiratory volume over one second (FEV1)105 Asthma symptoms and exacerbation89 Allergic responses with co-exposure to allergens37
Nitrogen dioxide (NO2)	Formed in high-temperature combustion processes, including power plants, traffic, and off-road vehicles131	Decreased lung function63,64 Allergic responses with co-exposure to allergens37
Sulfur dioxide (SO2)	Human sources include combustion of sulfur-containing fuels (such as coal) in power plants and other industrial process, metal extraction, and heavy vehicles132 Natural sources, including volcanic eruptions	Eye and upper airway irritation1 Alterations to lung function, loss of smell, headaches, dizziness, and decreased fertility133
Traffic-related air pollution (TRAP)	Combustion of diesel and gasoline in motor vehicles Significant sources include roadways, especially those with high traffic density	Decreased lung function63,64 Asthma symptoms and exacerbations89