English English

San Francisco’s continuing atmospheric angst enters its seventh straight day today, as the Environmental Protection Agency’s [EPA] AIRNow recorded some of the week’s worst air toxicity levels Thursday morning, with seemingly no end in sight.

The EPA scored San Francisco’s air at 177 on its 500-point Air Quality Index [AQI] as of 6 a.m. Thursday, which is still within the “unhealthy” spectrum of the scale due to the ongoing wildfires in Butte County.

Almost the entirety of the Bay Area is in poor condition, with areas around Livermore, Elk Grove, and Woodland in even worse shape, creeping up into the “very unhealthy” range.

According to the Bay Area Air Quality Management District:

The AQI numbers refer to specific amounts of pollution in the air. It’s based on the federal air quality standards for six major pollutants - ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and two sizes of particulate matter.

[...] Readings below 100 on the AQI scale should not affect the health of the general public (although readings in the moderate range of 50 to 100 may affect unusually sensitive people).

Levels above 300 rarely occur in the United States, and readings above 200 have not occurred in the Bay Area in decades.

The very young, the elderly, or those with preexisting respiratory illnesses are likely to find breathing troubles severely exasperated by smoke conditions.


The peer-reviewed American Journal of Medical Sciences examined some of the potential effects of exposure to pollutants in a 2007 report, noting:

Ambient NO2 exposure may increase the risk of respiratory tract infections through the pollutant’s interaction with the immune system.

Sulfur dioxide (SO2) contributes to respiratory symptoms in both healthy patients and those with underlying pulmonary disease.

Controlled human exposure studies have demonstrated that experimental SO2 exposure causes changes in airway physiology, including increased airways resistance. Both acute and chronic exposure to carbon monoxide are associated with increased risk for adverse cardiopulmonary events, including death.

However, studies have not demonstrated a clear dose-dependent health risk response to increasing amounts of these pollutants except at high concentrations.

Despite those ambiguities, there’s no doubt that prolonged exposure to higher concentrations of pollutants in wildfire smoke is unhealthy in the long run.

The day’s forecast indicates that conditions will slightly improve in the South Bay around San Jose, but worsen around the Santa Rosa area as the day progresses.

Go to top