The Air District is now accepting applications for its new zero-emission transport refrigeration unit, or TRU, funding program, aimed at reducing air pollution from diesel-powered refrigeration units used in the transport of perishable goods.
Learn about Napa County - its climate, potential air pollution concerns, and current air quality. You can also view upcoming Air District events in Napa County and read about local efforts to improve air quality.
Napa County is nestled in a valley between the Maycamas Mountains in the west and the Vaca Mountains in the east. One Napa County representative sits on the Air District’s Board of Directors.
The Air District is now accepting applications for its new zero-emission transport refrigeration unit, or TRU, funding program, aimed at reducing air pollution from diesel-powered refrigeration units used in the transport of perishable goods.
The Air District has issued 3 Notices of Violation to Valero for violations of air quality regulations and/or permit conditions for the May 5 fire. This is an ongoing investigation, and more violations may be issued.
The Air District is issuing an air quality advisory for smoke in Southern Solano, northern Contra Costa, and northwestern Alameda counties, specifically communities between I-80 and I-680 bridges (Martinez, Pacheco, Concord and Port Chicago), but with some impact possible southward to Oakland, due to a fire at Valero.
The Air District is announcing the start of the Spare the Air summer smog season, which runs from May to October in the Bay Area.
April 23, 2025
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The mountains bordering Napa Valley block much of the prevailing northwesterly winds throughout the year. Sunshine is plentiful in Napa County, and summertime can be very warm in the valley, particularly in the northern end. Winters are usually mild, with cool temperatures overnight and mild-to-moderate temperatures during the day. Wintertime temperatures tend to be slightly cooler in the northern end of the valley. Winds are generally calm throughout the county. Annual precipitation averages range from about 24 inches in low elevations to more than 40 inches in the mountains.
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.
In Napa County, ozone rarely exceeds health standards, but PM2.5 occasionally does reach unhealthy concentrations. There are multiple reasons for PM2.5 exceedances in Napa County. First, much of the county is wind-sheltered, which tends to trap PM2.5 within the Napa Valley.
Second, much of the area is well north of the moderating temperatures of San Pablo Bay and, as a result, Napa County experiences some of the coldest nights in the Bay Area. This leads to greater fireplace use and, in turn, higher PM2.5 levels. Finally, in the winter easterly winds often move fine-particle-laden air from the Central Valley to the Carquinez Strait and then into western Solano and southern Napa County.
Last Updated: 4/21/2017