Air Quality: Ozone

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. Ground-level ozone is formed from the reaction of oxygen-containing compounds with other air pollutants in the presence of sunlight.The main sources of ozone are trucks, cars, planes, trains, factories, farms, construction,and dry cleaners.

Why is this indicator 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.

What measure is used to evaluate ozone in CalEnviroScreen 4.0?

The California Air Resources Board maintains air monitoring data for ozone at a large number of air monitoring stations across the state.
Daily maximum 8-hour ozone concentrations were extracted from the air monitors for 2017-2019.
The mean of the summer months (May-October) was calculated by averaging across the three years.
A spatial model was created with the air monitoring data to estimate ozone concentrations for each census tract within 50 km of an air monitoring station.
For census tracts further than 50 km of an air monitor, the ozone value of the nearest monitor was used.
A complete description of the Ozone indicator is contained in the CalEnviroScreen 4.0 report.