Chileno Fire Smoke Triggers Air Quality Advisory Across Sonoma and Marin Counties

A wildfire that started around 4:40 p.m. on Sept. 20 in Chileno Valley, near the Marin-Sonoma county line, sent enough smoke into the North Bay that the Bay Area Air Quality Management District (BAAQMD) issued a smoke advisory for Sonoma and Marin counties, warning that smoke could spread into Napa and Solano counties as well. The Chileno Fire burned a combined 340 acres, and crews stopped its spread shortly before 7 p.m. that evening, according to the Press Democrat.

What the advisory said

BAAQMD’s advisory, issued Sept. 20, said pollutant levels were not expected to exceed the national 24-hour health standard — meaning no Spare the Air Alert was triggered. That distinction matters: an advisory flags localized, visible smoke impacts, while a Spare the Air Alert reflects a forecast that regional particulate levels will cross a formal health threshold.

Who should take precautions

BAAQMD’s guidance, standard for wildfire smoke events, recommended that North Bay residents:

• Stay inside with windows and doors closed if possible
• Set vehicle ventilation to recirculate mode when driving through smoky areas
• Use indoor air filtration, or visit a local Clean Air Center if available
• Take extra precautions for older people, children, and anyone with respiratory conditions

The fire itself

The Chileno Fire burned along Chileno Valley Road, about four miles south of Tomales Road. It was actually several fires: crews halted one smaller fire by 4:50 p.m. and stopped the other two just before 7 p.m., for a combined 340 acres. No evacuation orders or warnings were issued. Even so, smoke drifted toward Sonoma County, and shortly before 8 p.m. areas nearest the fire reported unhealthy air quality, while areas farther inland reported air that was unhealthy for sensitive groups or moderate. The cause had not been reported as of Sept. 21.

Why localized smoke events matter

Not every wildfire that generates an air quality advisory is large or long-burning. A few hundred acres burning close to a population center, under the wrong wind conditions, can produce more immediate smoke exposure for more people than a much larger fire burning in remote wilderness. That’s part of why air districts track smoke advisories separately from fire-size and containment statistics.

Figures as of Sept. 21, 2026

Acreage and advisory details reflect the most recent BAAQMD and local news reporting as of that date; both fire containment and air quality conditions can change quickly with wind shifts.

Checking conditions where you live

Real-time smoke and air quality data for any US location is available through the EPA’s AirNow Fire and Smoke Map. FireVerge’s guide to wildfire smoke and air quality explains how to interpret AQI categories and reduce smoke exposure at home, and our California state page tracks wildfire activity and smoke trends across the state.