Definition: Annual average concentration of fine particulate matter in the air (e.g., in 2019, the average concentration of fine particulate matter in the air in Los Angeles County was 11 micrograms per cubic meter).
Data Source: California Air Resources Board, iADAM: Air Quality Data Statistics; U.S. Environmental Protection Agency, Particulate Matter (PM2.5) Trends (Dec. 2020).
Footnote: 'Fine particulate matter' (PM2.5) refers to particles with a diameter of less than 2.5 microns. PM2.5 is an air pollutant commonly found in diesel exhaust. The national ambient air quality standard for PM2.5 is 12 micrograms per cubic meter (µg/m³); annual concentrations above 12 µg/m³ are considered unhealthy, especially for sensitive groups such as children, asthmatics, and the elderly. Data are limited because (i) monitoring stations are usually in urban areas, and (ii) PM2.5 samples are taken every three days or during times of the year when air pollution is very high. In addition, not all counties are monitored, and data are only provided for counties with monitors that meet completeness criteria. State-level data are averaged from county-level data and should be treated with caution. N/A means that data are not available.
