Update, August 24: Friday morning the air had cleared a bit in San Francisco and most of the East Bay but considerably worsened in the South Bay.
The EPA’s AIRNow site indicates unhealthy air conditions in and around San Jose and Livermore, while air quality in SF and most of the rest of the Bay Area hovers in the “moderate” designation.
Note that Thursday’s warning is still in effect at least throughout the rest of Friday and that air quality in SF and surrounding areas may diminish as the day continues.
The Bay Area Air Quality Management District [BAAQMD] issued an advisory late Thursday afternoon warning that smoke from California wildfires had created unhealthy atmospheric conditions in San Francisco and the surrounding area.
The BAAQMD Spare the Air Warning is in effect at least through Friday. During summer Spare the Air Days, the district advises:
Avoid physical outside activities and don’t let your children play outdoors. [...] If you are advised to stay indoors, keep indoor air as clean as possible. Keep your windows and doors closed unless it’s extremely hot outside. If you don’t have an air conditioner, staying inside with the windows closed may be dangerous in extremely hot weather. In these cases, seek alternative shelter.
Even if the air does not appear visibly worse in your area, take the advised precautions just in case. Children, the elderly, and those with already compromised respiratory systems are especially vulnerable.
According to the EPA’s air quality monitoring site AIRNow, conditions in San Francisco, Alameda County, and large parts of Contra Costa County and San Mateo County are “unhealthy,” hitting the 150-200 range on the EPA’s 500 point hazardous air scale.
For perspective, most days San Francisco’s air quality falls neatly within the 0-50 range, dubbed “good.” Days when hazardous air peaks into the 50-100 range, or “moderate,” are comparably rare.
The “unhealthy” threshold usually comes in the city only a few times a year.