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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
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Air District fines Chemtrade West US LLC $160,000 for air quality violationsSeptember 02, 2025
The Air District has fined Chemtrade West US LLC $160,000 for air quality violations at its sulfuric acid manufacturing plant in Richmond, which is connected to the Chevron Richmond refinery. Chemtrade supplies various chemical products to industry, including sulfuric acid, which is a byproduct of refining crude oil.
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Air District lifts air quality advisory for wildfire smokeAugust 26, 2025
The Air District is lifting an air quality advisory for wildfire smoke that was originally scheduled to last through tomorrow, Wednesday, August 27.
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Air District awards $13.3 million to SamTrans toward the installation of new zero-emission bus charging infrastructureAugust 26, 2025
The Air District has announced a $13.3 million grant to the San Mateo County Transit District toward the installation of new high-capacity electric bus charging infrastructure at its San Carlos facility. This SamTrans project will help accelerate the transition of the SamTrans bus fleet to zero-emission technology and improve air quality in communities most affected by air pollution.
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Upcoming Events
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SEP162025
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SEP172025
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SEP172025
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SEP182025
Other News Articles
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8/21/2025 Air District issues air quality advisory for wildfire smoke through Friday
August 21, 2025
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8/19/2025 Air District and Tesoro reach $75,000 settlement with enhanced requirements for air monitoring and transparency
August 19, 2025
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8/18/2025 Air District directs Crown Hill Materials to cease operating unpermitted concrete batch plant
August 18, 2025
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8/14/2025 Air District files lawsuit against Acme Fill Corporation for illegal landfill emissions
August 14, 2025
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8/12/2025 Air District issues air quality advisory for wildfire smoke for Tuesday
August 12, 2025
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8/11/2025 Air District reaches agreement with Argent Materials to resolve air quality violations
August 11, 2025
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7/30/2025 Deadline to apply for the Air District’s Clean HEET program extended
July 30, 2025
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7/28/2025 Air District awards $3.5 million in second cycle of James Cary Smith Community Grant Program
July 28, 2025
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7/23/2025 Air District urges Bay Area to proactively prepare for smoke this wildfire season
July 23, 2025
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7/17/2025 Air District and Alameda County District Attorney announce enforcement actions against Radius Recycling, formerly Schnitzer Steel
July 17, 2025
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7/14/2025 Air District lifts air quality advisory for wildfire smoke for Monday
July 14, 2025
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.
Climate
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.
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.
Spare the Air Status
Last Updated: 4/21/2017