Things weren't quite as orange on Thursday morning as they were a day earlier, though the sky may look like that again before all this is through. And unlike yesterday when ground-level air quality was fairly okay, today's not a day to be walking outside or exercising.
You may have found some ash on your deck or car yesterday, as bits of the wildfires to our north and northeast rained down on San Francisco and the surrounding area. But those larger particles — 10 microns or greater — are not so bad when it comes to breathing them in according to Dr. Mary Prunicki, Stanford Director of Air Pollution and Health Research. As she tells KPIX, "We can inhale those and they can only go part way down our respiratory system. They get stuck midway down because of their size."
It's the finer particles from smoke and pollution that are a lot more dangerous to human health, and that's what we're seeing more of today. The Air Quality Index (AQI) for San Francisco was between 175 and 200 as of 10 a.m., which puts the city in the "red" or unhealthy zone — basically you shouldn't be outside without an N95 mask.
Roger Gass, a meteorologist with the National Weather Service, tells the Chronicle Thursday morning that a thicker marine layer moved in over the Bay overnight and that is likely responsible for the less colorful sky today. And he adds that the fog is at least providing some much needed moisture to dry hills where firefighters are still trying to contain the remnants of nearly 30-day-old wildfire complexes around the region.
The sun-obscuring smoke is likely to stick around through Friday barring a sudden shift in winds, but the AQI is forecast to improve over the course of Thursday, according to the EPA's AirNow site. By later today, SF is supposed to return to "yellow" or "moderate" territory, and most of you can go back to exercising outdoors.
Here's a forecast that goes into Friday showing heavy smoke lingering.