List of information sources about the California fires, air quality & preventative actions for your health. :

The air quality in the Bay Area (San Francisco) and North Bay Area (Sonoma, Napa) today is in the red and deep red zone:

https://airnow.gov/index.cfm?action=airnow.local_city&zipcode=94110&submit=Go

From an official government page in case the air quality declines further, preventative actions to take:
https://airnow.gov/index.cfm?action=aqibasics.pmhilevels

Here something about breathing masks, it is recommendable to use them, the smoke particles are microparticles that are harmful to lungs and health:
https://www.doh.wa.gov/Portals/1/Documents/Pubs/334-353.pdf

Where you can buy breathing masks (check the link about breathing masks above before buying): This is a link to masks on Amazon, select the quickest delivery option in case the fires will continue to burn for a while longer. Protect your lungs.

Here updates directly from Sonoma:
https://www.facebook.com/CityOfSonoma/

The active wildfire map, where you can check where there are active wildfires in America, updated frequently:
https://www.arcgis.com/home/webmap/viewer.html?webmap=df8bcc10430f48878b01c96e907a1fc3

Click on the map to open the current Air Quality Window

The air quality in San Francisco is already in the RED zone. This means that it already can cause noticeable health reactions. However don’t panic: keep physical activity to a minimum, stay indoors as much as possible. As a tourist: these are the days for museum visits and spending time in cafes and aquariums.

In the North Bay the air quality is in the DEEP RED zone = very bad, it is strongly advisable to not expose yourself unnecessarily. Many people will notice negative effects on their health at those levels. Use the first link in this post to enter the postcode of where you re to check your aibquality and read all the links to thorough information.

RED::
AQI: Unhealthy (151 – 200)
Everyone may begin to experience health effects members of sensitive groups may experience more serious health effects.

DEEP RED:
AQI: Very Unhealthy (201 – 300)
Health alert: everyone may experience more serious health effects.