According to the EPA’s AirNow site, air quality in San Francisco today is expected at around 68 on the federal Air Quality Index, which qualifies as “moderate” and yields a warning that “unusually sensitive people should consider reducing prolonged or heavy exertion.”
“Unusually vulnerable” in this context generally means young children, the elderly, or anyone with chronic respiratory problems already. This level of air pollution is not usual for San Francisco, but neither is it particularly alarming.
However, conditions will significantly worsen over much of Contra Costa and Santa Clara Counties as the day goes on, and the forecast holds that air quality will creep up into the “Unhealthy For Sensitive Groups” range, meaning:
Although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air.
On days like today, the district advises residents to “cut back on any activities that cause pollution such as driving, using oil-based paints, gasoline-powered lawn mowers, or household aerosol products like hair sprays” and to try to keep indoors if possible, especially in the afternoon.
Although air quality always has its ups and downs even in the usually pristine Bay Area, there’s no secret why things have turned to worse this week, as smoke from Northern California wildfires drifts over the rest of the state, lending a telltale ashy odor to the air at times.
So far this year there have been five Spare the Air declarations in the Bay Area. In 2017 there were 18 and in 2016 there were 27, outstripping the 20 year average of 10.3.