With Fall Comes Easterly Winds, Fires and Smoke in Northern California

Here in San Francisco, we can sometimes take our typically excellent air quality for granted.  Occasionally, when a high-pressure weather system parks over the Bay Area, a dome of sinking air will block the fresh ocean breezes and trap all the car exhaust and industrial pollution near the surface and we’ll get a “spare the air” alert. Usually, communities can prevent an unhealthy build-up of air pollution by minimizing driving, wood burning, or use of gas-powered equipment and a few days later our natural air conditioning kicks back in the form of sometimes bone-chilling westerly winds off the Pacific to clean everything up by blowing the pollution to the east.

But in fall, our winds shift, blowing from the north or east, drying out the air and creating dangerous fire conditions. This year the danger was more pronounced because of the drying effect of recent heat waves over a dense growth of grasses and shrubs from heavy winter rains months ago. Just as feared, a devastating set of fires broke out and spread to our north, impacting air quality all over the Bay Area depending on the wind direction and proximity to the fires. California has an air quality index website that tracks healthy to unhealthy air masses throughout the state, called "AirNow". When the air quality deteriorates like it has this week in San Francisco, officials recommend that children, older adults, and those with heart or lung disease avoid exposure and that everyone else limit their outdoor exercise or even wear masks to block soot particles. (In and around Sonoma County, the air quality index is unhealthy or very unhealthy for everyone and dangerous for sensitive groups).

The Wired Pier sensors on our roof, part of UC Berkeley’s BEACON network, also recorded elevated levels of particulates at Pier 15. The fires broke out overnight on October 8^th, and we saw the levels of ash and smoke particles jump on the 10^th and 11^th.

Click here to explore this data interactively.

The BEACON network as a whole showed how wind on October 10^th was a big factor for which Bay Area communities had the worst air quality—the biggest effect was closest to the fires but you can see the direction that the winds have been blowing from this map provided by Alexis Shusterman and Ron Cohen, who operate the entire BEACON network.

Of course, we are all deeply concerned about our friends and neighbors who have lost property and loved ones in the fires. It’s an eerie sight to see a blood orange sunrise and thick smoke across our bay and valleys. Burning eyes and raw throats are a constant reminder of how much the fires are still raging nearby and, with low humidity and tinder-dry vegetation, the threat for more is all around. But with luck, our moist winds will return, perhaps even some rain to help the firefighters. With time, those displaced by fires can return and rebuild their lives, and we can breathe in clean ocean air once again.