Air Quality

I-5 Freeway

Current Air Quality Index

Historical Air Quality Index​

The EPA tracks air quality under the Air Quality Index (AQI) measurement based on the number of air pollutants. Scores are between 0 and 500: 0–50 is GOOD, 51–100 MODERATE, 101–150 UNHEALTHY FOR SENSITIVE GROUPS, and 151+ is UNHEALTHY. 



This graph shows ground-level ozone concentration trends for Merced, Stanislaus, and San Joaquin counties. Ground level ozone, a secondary pollutant, occurs when two primary pollutants (nitrogen oxide and volatile organic compounds) react in sunlight and stagnant air. Ozone levels overall have trended downward; San Joaquin County has had the lower overall levels since 1991. CBPR obtained this data from the California Air Resources Control Board, California Almanac of Emissions and Air Quality (Source: UOP CBPR Index).

Asthma and Air Quality

Asthma and air quality are related. Although the region’s unhealthy ozone days have fallen 41% since 2000, the region contains some of the U.S.’s most polluted air. According to the American Lung Association, San Joaquin County ranked ninth in the nation for particulate matter in 2015. More than 27% of San Joaquin County Community Health Needs Assessment survey respondents reported breathing problems as a top community health concern, and 39% of respondents claimed air pollution as a major environmental concern.

As this graph shows, the percentage of children age 1–17 whose parents report an asthma diagnosis is almost 20% higher than that of California. And San Joaquin County adult asthma diagnoses are 7% higher than California.