The Air District is issuing its second Spare the Air Alert of the year for ozone for Tuesday, September 23.
Learn about Santa Clara County - its climate, potential air pollution concerns, and current air quality. You can also view upcoming Air District events in Santa Clara County and read about local efforts to improve air quality.
The Air District is issuing its second Spare the Air Alert of the year for ozone for Tuesday, September 23.
The Air District has awarded $1.18 million grant to the San Ramon Valley Unified School District to replace seven older school buses, five compressed natural gas buses and two diesel buses with zero-emission electric buses and the charging infrastructure to support them. The project will also support the installation of eight DC fast chargers and related infrastructure.
The Air District has relaunched its Clean Cars for All program with more than $10 million available from state and local funding sources for income-qualified Bay Area residents to purchase cleaner air vehicles.
Changes focus on improving efficiency and delivering timely, transparent permit decisions.
August 25, 2025
August 23, 2025
August 22, 2025
August 21, 2025
August 19, 2025
August 18, 2025
August 14, 2025
August 12, 2025
August 11, 2025
July 30, 2025
July 28, 2025
July 23, 2025
July 17, 2025
July 14, 2025
Santa Clara County is south of the San Francisco Bay, with San Mateo and Alameda counties bordering it to the north, Santa Cruz County to the west, San Benito County to the south, and Stanislaus and Merced counties to the east. Four Santa Clara County representatives sit on the Air District’s Board of Directors.
During the summer, mostly clear skies result in warm daytime temperatures and cool nights. Winter temperatures are mild, except for very cool but generally frost-less mornings.
Further inland where the moderating effect of the bay is not as strong, temperature extremes are greater. Wind patterns are influenced by local terrain, with a northwesterly sea breeze typically developing during the daytime. Winds are usually stronger in the spring and summer. Rainfall amounts are modest, ranging from 13 inches in the lowlands to 20 inches in the hills.
Interactive Air Monitoring Stations Map
Ozone and fine particle pollution, or PM2.5, are the major regional air pollutants of concern in the San Francisco Bay Area. Ozone is primarily a problem in the summer, and fine particle pollution in the winter.
Most of Santa Clara County is well south of the cooler waters of the San Francisco Bay and far from the cooler marine air which usually reaches across San Mateo County in summer. Ozone frequently forms on hot summer days when the prevailing seasonal northerly winds carry ozone precursors southward across the county, causing health standards to be exceeded.
Santa Clara County experiences many exceedances of the PM2.5 standard each winter. This is due to the high population density, wood smoke, industrial and freeway traffic, and poor wintertime air circulation caused by extensive hills to the east and west that block wind flow into the region.
Last Updated: 4/21/2017