2020, meanwhile, was a record-setting year for wildfires in the Pacific West, including California. Notably, while wildfires in 2019 were less severe and less frequent than in the previous 5 years, they still comprised a major source of statewide air pollution. In 2019, 19 of the 20 most polluted cities in the United States for PM2.5 pollution were in California, where wildfires contributed to heightened monthly averages. Since 1970, the number of annual burned acreage has risen eightfold, while over the same time period summer temperatures have increased by 2.5 degrees. Increasingly hot and dry conditions have drastically increased the threat of California wildfires. In addition to ozone, warming temperatures have also contributed to California’s rising PM2.5 levels. As summer temperatures rise, as they have in recent years, so too do California’s ozone levels. Warm temperatures and abundant sunshine, for which California’s coast is known, bake nitrogen oxides and volatile organic compounds, creating ozone. Without a means for dispersion, pollution accumulates in the coastal valleys. Here, westerly sea breezes can create a pollution-trapping effect in which emissions blown inland become trapped by the mountains, inversion layers, and stagnant air. Locations in or near the Klamath, Sierra-Nevada, and Coastal mountains, among numerous other mountainous areas, are more likely to experience elevated pollution levels as a result of wildfires, despite having less pollution most of the year.Ĭalifornia’s most populous cities, including Los Angeles, San Diego, San Jose, and San Francisco, are all located near California’s coastal mountain ranges. Areas of relatively dense populations often experience higher daily pollution levels as a result of increased traffic, industry, and domestic emissions. Sources of air pollution in California include vehicular emissions, demand for energy production through fossil fuels, and household energy consumption as well as wildfires as a prominent natural cause. Why do parts of California have such bad air pollution? Follow health recommendations when air quality levels exceed “good” standards. Use the IQAir California air quality map to discover air pollution levels across the state and help attribute city air quality to the emission source.

A 2010 study conducted by the California Air Resources Board estimates that PM2.5 pollution causes over 9,200 deaths in California annually, with a statistical range from 7,300 to 11,000 deaths. Cities from Los Angeles to San Francisco experienced numerous days of sustained unhealthy air quality levels.īreathing air pollution can be fatal, and higher air pollution levels increase the risk of adverse health effects. The wildfire season of 2020 constituted some of the most severe wildfires in recent years, raising pollution levels far above typical local ranges. Such a progression is likely to worsen California air quality levels. Human-driven climate change is expected to further aggravate the intensity of wildfires in the future by creating warmer and drier conditions. While wildfires represent a temporary emission source, their impact on monthly and yearly air pollution averages can be severe. In any given year, California’s most polluted cities tend to be cities most affected by that year’s wildfire season. Environmental conditions, which are prone to frequent and severe wildfires, with mountainous terrain that traps pollution, and a warm climate that contributes to ozone formation, present additional challenges to California's air quality.

The state’s large population of 39 million, significant port industry, and growing economy create significant emissions by way of traffic, diesel trucks, construction, agriculture, and domestic emissions. The top five cities in the country with the worst annual PM2.5 levels are all located in the state, including Bakersfield, Fresno-Madera-Hanford, Visalia, Los Angeles-Long Beach, and San Jose-San Francisco- Oakland.Ĭalifornia also holds all of the top five cities in the country for worst ozone, including Los Angeles-Long Beach, Visalia, Bakersfield, Fresno-Madera-Hanford, and Sacramento-Roseville.Ĭalifornia’s unhealthy air quality, relative to other US states, is the result of a combination of factors. Only 35.7 percent of cities met the World Health Organization (WHO) target for annual PM2.5 exposure of 10 μg/m 3, as compared to the national average of 81.7 percent.Īccording to the American Lung Association's recent 'State of the Air 2019' report, California leads the charts for cities with the worst air pollution. Why does California have the worst air quality?Īcross 112 cities, California averaged a PM2.5 concentration of 12.1 μg/m 3 (“moderate”) in 2018.