About the Air District

San Mateo County

Learn about San Mateo County - its climate, potential air pollution concerns, and current air quality. You can also view upcoming Air District events in San Mateo County and read about local efforts to improve air quality.

Latest News
  • Oct

    October 14, 2021

    Air District to provide home air filtration units in West Oakland

    The Air District is working with the West Oakland Environmental Indicators Project and the West Oakland Health Council, through the Clean Air Filtration Program, to provide portable air filtration units to low-income residents of West Oakland diagnosed with a respiratory illness.

  • Oct

    October 6, 2021

    Air District relaunches Clean Cars for All program on Clean Air Day

    The Air District has relaunched its Clean Cars for All program with more than $8 million available for qualified residents to purchase a clean air vehicle. 

  • Oct

    October 3, 2021

    Air District issues air quality advisory for Monday

    The Air District is issuing an air quality advisory for wildfire smoke for Monday, October 4. Smoke from wildfires in Southern California is expected to continue impacting the Bay Area on Monday with smoky and hazy skies. Pollution levels are not expected to exceed federal health standards and no Spare the Air Alert is in effect for Monday. A Spare the Air Alert for ozone, or smog, remains in effect for Sunday, October 3.

San Mateo County lies in the middle of the San Francisco Peninsula, south of San Francisco County, and north of Santa Clara and Santa Cruz counties. It is bounded by the Pacific Ocean to the west and San Francisco Bay to the east. Two San Mateo County representatives sit on the Air District’s Board of Directors.


Cool, foggy weather is prevalent along the western coast of the peninsula, particularly during the summer. Summertime average daily temperatures are moderate along the west coast and warm in the county’s east side. In the winter, average daily temperatures across the county range from mild to moderate. Winds are mild, with the highest wind speeds focused along the western coast. Rainfall averages about 20 to 25 inches per year at lower elevations and up to 36 inches in the Santa Cruz Mountains.

San Mateo County's climate is also affected by regional Bay Area climate influences.

Interactive Air Monitoring Stations Map

Air Quality in San Mateo County

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.

In San Mateo County, ozone almost never exceeds health standards, and PM2.5 exceeds the national standard only on about one day each year. San Mateo County frequently receives fresh marine air from the Pacific Ocean, which passes over the coastal hills. In winter, PM2.5 may be transported into San Mateo County from other parts of the Bay Area, adding to wood smoke, which may lead to elevated concentrations, but these are rarely high enough to exceed health standards.

Interactive Air Quality Forecast Map

Resource Team

San Mateo County's Spare the Air Resource Team promotes ways to reduce air pollution in the local community.

Spare the Air Status

Last Updated: 2/14/2019