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Air District Fact

The Air District holds many community meetings on air quality topics. Most of these are informational in nature, where The District asks for input on activities and answers questions on such topics as regulationsclean air plans and strategies and issues of interest to a the community.

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BAAQMD Webcasts

Upcoming Webcasts

Workshop on Proposed Amendments to Regulation 2: Permits to be Webcast live from 10:00am to 12:00pm on 2/22/2012.
More Information:
Workshop Notice
(521 k PDF, 5 pgs)
Rule Workshops

Recent Webcasts

The Particulate Matter Workshop is available as a Webcast archive.
Meeting Presentation:
Reducing Particulate Matter in the SF Bay Area
(4 MB PDF, 49 pgs)
More Information:
Particulate Matter Planning

12/14/2011 Board of Directors Special Meeting
More Information:
12/14/2011 Agenda
(545 k PDF, 23 pgs)
Board Archives:
Agendas, Minutes and Media

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Largescale Influences

The summer climate of the West Coast is dominated by a semipermanent high centered over the northeastern Pacific Ocean. Because this high pressure cell is quite persistent, storms rarely affect the California coast during the summer. Thus the conditions that persist along the coast of California during summer are a northwest air flow and negligible precipitation. A thermal low pressure area from the Sonoran-Mojave Desert also causes air to flow onshore over the San Francisco Bay Area much of the summer.

The steady northwesterly flow around the eastern edge of the Pacific high pressure cell exerts a stress on the ocean surface along the west coast. This induces upwelling of cold water from below. Upwelling produces a band of cold water that is approximately 80 miles wide off San Francisco. During July the surface waters off San Francisco are 30F cooler than those off Vancouver, more than 700 miles farther north.

Air approaching the California coast, already cool and moisture-laden from its long trajectory over the Pacific, is further cooled as it flows across this cold bank of water near the coast, thus accentuating the temperature contrast across the coastline. This cooling is often sufficient to produce condensation -- a high incidence of fog and stratus clouds along the Northern California coast in summer.

In winter, the Pacific High weakens and shifts southward, upwelling ceases, and winter storms become frequent. Almost all of the Bay Area's annual precipitation takes place in the November through April period. During the winter rainy periods, inversions are weak or nonexistent, winds are often moderate and air pollution potential is very low. During winter periods when the Pacific high becomes dominant, inversions become strong and often are surface-based; winds are light and pollution potential is high. These periods are characterized by winds that flow out of the Central Valley into the Bay Area and often include tule fog.

Last Updated: 10/4/2010