As six of the largest 20 fires in California history poured smoke into the atmosphere in recent weeks, and new fires were sparked in Oregon and Washington, the skies over the Bay Area and beyond were blanketed in smoke and at times turned unnerving shades of orange. Reports of ash falling flooded social media as entire towns were evacuated due to the fires.

Early Tuesday morning in San Francisco, a massive five-alarm fire erupted in a building supply company according to the San Francisco Fire Department (SFFD). Smoke from the fire rose in a plume high above ground level and was blown northeastward by the winds aloft. Aclima’s network of mobile and stationary air quality sensors picked up the local spikes in fine particulate matter (PM₂.₅) in the hours after the fire began. We continued to see elevated PM₂.₅ levels — particularly in the East Bay — until the valiant and commendable people of the SFFD all but extinguished it midday. However, firefighters remain on the scene as the debris continues to burn.