Table 1.
Size and composition of air pollutants.
| Pollutant | Source | US Levels | US Air Quality Standard | Reference |
|---|---|---|---|---|
| PM2.5 | Combustion sources (e.g. vehicle emissions and industrial processes) Natural causes (e.g. wildfires) Atmospheric photochemical reactions with gaseous pollutants such as NOx, O3, SO2, CO, and VOCs |
10.40 μg/m3 (2000–2019) 8.57 μg/m3 (2010–2019) |
12 μg/m3 (annual mean) 25 μg/m3 (24-hour mean) |
Brandt et al. (2020) Health effects of particulate matter (2013) |
| PM10 | 79.49 μg/m3 (2000–2019) 75.13 μg/m3 (2010–2019) |
No annual mean 150 μg/m3 (24-hour mean) |
Brandt et al. (2020) California Air Resources Board (2020) |
|
| PM0.1 (UFPs) | 4730 particles/cm3 | 10,760 particles/cm3 |
Brandt et al. (2020) Morawska et al. (2008) |
|
| NO2 and other NOx | Combustion sources Conversion from NO by atmospheric O3 |
44.45 ppb (2000–2019) 37.29 ppb (2010–2019) |
40 μg/m3 (annual mean) 200 μg/m3 (1-hour mean) |
“Basic Information about NO2” (2016) Brook et al. (2004) U.S. Environmental Protection Agency (2016) |
| O3 | Atmospheric photochemical reactions with oxygen, NOx, and reactive hydrocarbons in sunlight | 0.074 ppm (2000–2019) 0.068 ppm (2010–2019) |
100 μg/m3 (8-hour mean) | U.S. Environmental Protection Agency (2015) |
| CO | Vehicle emissions Incomplete combustion of organic fuels (e.g. gasoline, oil, and coal from vehicles and other fossil fuel combustion sources) |
1.88 ppm (2000–2019) 1.26 ppm (2010–2019) |
9 ppm (8-hr mean) |
“Carbon Monoxide Trends” (2016) U.S. Environmental Protection Agency (2016) |
| SO2 | Burning of fuel containing sulfur (e.g. coal and oil in power plants, vehicles, and volcanoes) Reacts with water to form sulfuric acid |
47.33 ppb (2000–2019) 25.84 ppb (2010–2019) |
20 μg/m3 (annual mean) 500 μg/m3 (10-minute mean) |
U.S. Environmental Protection Agency (2016) |
| VOC (e.g. formaldehyde and benzene) | Mostly indoor burning of fuels, organic chemicals in household products | 0.1–1 ppb | N/A | Pankow et al. (2003) |
Only the most representative citations are given. (PM, particulate matter; PM2.5, particles with a diameter ≤ 2.5 μm; PM10, particles with a diameter ≤ 10 μm; PM0.1, particles with a diameter ≤ 2.5 μm; NO2, nitrogen dioxide; NOx, nitrogen oxides; O3, ozone; CO, carbon monoxide; SO2, sulfur dioxide; VOC, volatile organic compounds; μg/m3, micrograms per meter cubed; ppm, parts per million; ppb, parts per billion.)