Air Quality: Ozone
Exposure Indicator
Measures ground-level ozone concentrations that communities are exposed to—one of California's most widespread air pollution health threats.
What is ozone?
Ozone is the main ingredient of smog. At ground level, ozone is formed when pollutants chemically react in the presence of sunlight. The main sources of ozone are trucks, cars, planes, trains, factories, farms, construction, and dry cleaners.
Why is it included in CalEnviroScreen?
- Ozone is among the most widespread and significant air pollution health threats in California and is one of the US Environmental Protection Agency's six commonly found “criteria” air pollutants.
- Ozone can cause lung irritation, inflammation, and worsening of existing chronic health conditions, even at low levels of exposure.
- Children are most sensitive to the effects of ozone exposure. The elderly and people who spend a lot of time outdoors are also sensitive.
- Studies have shown that ozone can increase asthma emergency room visits among children and can increase mortality, especially in the elderly, women, and African Americans.
- Ozone levels are typically highest in the afternoon and on hot days.
How is it measured?
- The California Air Resources Board measures ozone concentrations from a wide network of air monitoring stations across the state.
- Daily maximum 8-hour ozone concentrations were extracted from the air monitors for the summer months (May–October) for the years 2022–2024.
- The mean of the summer months was calculated by averaging the daily maximum 8-hour ozone concentrations over those three years.
- A spatial interpolation model (ordinary kriging) was used to estimate ozone concentrations for the center of each census tract across the state.
