A thick haze settled over Walnut Creek on Tuesday, Aug. 25, prompting a wave of calls from residents who smelled smoke and feared a local fire. There wasn't one.
Local fire crews dispatched to neighborhoods generating the most calls found no active fires, News24-680.com reported. The smoke was eventually traced to prescribed burns in Marin County, where the Marin County Fire Department and Marin Water were burning vegetation near Sky Oaks Ranger Station on Mount Tamalpais.
An inversion layer trapped the smoke low and wind pushed it east into the Highway 24/680 corridor, according to News24-680.com. Purple Air sensor readings showed the haze concentrated tightly over Lamorinda, Walnut Creek, Pleasant Hill and Concord, while areas just outside that band stayed clear.
What was burning in Marin
The Marin County Fire Department conducted the first of two planned burns Tuesday in the Mt. Tamalpais Watershed west of Fairfax, according to a joint news release from the county and Marin Water. The burn covered up to 79 acres south of Sky Oaks Ranger Station between Bullfrog Road and Bon Tempe Road. A second burn covering up to 44 acres near Bon Tempe Reservoir was planned for Wednesday, Aug. 26.
Both burns are part of ongoing vegetation management on the mountain. The Marin County Fire Department said in the release that operations would strictly adhere to Bay Area Air Quality Management District requirements, but warned that surrounding communities might still smell or see smoke.
Why Walnut Creek got the worst of it
News24-680.com noted this is not the first time distant fire smoke has been pulled into the 24/680 corridor under similar inversion conditions.
The Orinda Flashers community alert network was first to flag the smoke's arrival Tuesday afternoon. Reports spread quickly through Lafayette, Walnut Creek and Concord.
"Crazy how that smoke is pulled into these valleys."
One commenter on News24-680.com captured the surprise many residents felt watching the haze roll in despite no local burn activity.
What residents should know
The Marin County Fire Department asked the public not to call 911 to report smoke from prescribed burns, so dispatchers remain available for actual emergencies. Residents who want advance notice of future burns can subscribe to AlertMarin at Emergency.MarinCounty.gov.
For air quality monitoring, the Walnut Creek School District uses AirNow.gov as its primary measurement tool and has upgraded all school facilities with MERV 13 filters that capture PM2.5 smoke particles.
Residents can check real-time air quality readings at AirNow.gov or on Purple Air's sensor map.
