Locals have been wondering why the skies have been increasingly hazy in Downtown San Francisco and over the bay for the last few days—especially while air quality remains good.
San Franciscans are spoiled by clear blue skies and very good air quality when Karl isn’t around. The only times haze comes into the city is when wildfires are burning in the region or on cold winter days when smoke from wood fires causes air pollution.
“The air quality is ‘good’ for everyone in the Bay Area,” says Ralph Borrmann of the Bay Area Air Quality Management District, adding that parts of the Santa Clara Valley might be entering the “moderate” range because of rising temperatures.
So what’s the deal with the haze?
Borrmann says several factors can contribute to haze on a spring day.
First, the normal industrial output created by factories, traffic and refineries is always a factor in any metropolitan region. Second, winds from agricultural areas in California's Central Valley can bring dust to the Bay Area. Both of these factors produce large particles that remain high aloft, however, and wouldn’t likely be a big factor at sea level.
A more likely culprit, according to Borrmann, is the gusty winds that have been battering the Bay Area recently. Winds like these can bring sea spray off the Pacific and into the city, which can cause hazy skies, especially in bayfront areas.
What’s not causing the haze? The increasing amount of pollen in the air as a result of superblooms going on following winter rains. Borrmann says pollen is not a cause of air pollution and, therefore, not measured by the Bay Area Air Quality Management District.
Maryann Jones Thompson can be reached at [email protected]