As a weeklong, severe heat wave ends in northern California, mountain towns between Sacramento and Reno, Nevada are experiencing unhealthy to hazardous air quality.

While heat and an ongoing megadrought fueled fires throughout California on Thursday, September 8, lingering dry conditions in Washington state, Montana, and Idaho spurred wildfire growth in the mountains. Wildfire smoke in those states led to very unhealthy to hazardous air quality for residents across the western United States.

Sierra Nevada wildfire clouds communities in smoke

The Southwestern U.S. is in a 22-year "megadrought," the driest conditions experienced in the region in 1,200 years. Throughout 2022, most western states have endured extreme to exceptional drought, drying out brush and vegetation that a lightning strike can quickly turn into an inferno (1)(2).

Placer County, California is struggling with both a heat wave and extreme drought. Those conditions helped spark the 5,700-acre Mosquito fire, which caused evacuations and destroyed homes in the county, northeast of Sacramento (3)(4).

Wildfire smoke also created air pollution in Placerville County and neighboring El Dorado County. Measured concentrations of PM2.5 at Auburn Lake Trails was an unhealthy 105 micrograms per cubic meter of air (µg/m3)

Wildfire smoke carries airborne pollutants like PM2.5, particulate matter of less than 2.5 micrograms in diameter. Airborne PM2.5 is linked to lung and heart illness.

Dangerously high concentrations of PM2.5 were measured in mountain towns across the Sierra Nevada on Thursday morning. Some of the communities worst impacted by hazardous air quality included:

• Foresthill
• Cool
• Loomis
• Granite Bay
• Auburn

All top ten communities with exceptionally poor air quality in California were affected by nearby wildfire smoke. Source: IQAir.

Air quality monitors measured concentrations of PM2.5 in Loomis, California of 326 µg/m3, well into the hazardous range for the U.S. air quality index (AQI).

Air quality monitors detected concentrations of unhealthy to hazardous air quality in the Sierra Nevada mountain range. Source: IQAir.

Heat wave sparks Southern California wildfires

The California heat wave ignited two deadly fires in arid back country far east of Los Angeles.

Smoke from the Fairview fire severely impacted air quality in Hemet, a rural town in Riverside County, California. Concentrations of PM2.5 in Hemet measured 217 µg/m3.

Two people were killed and a third severely injured while trying to escape the fast-moving fire, which exploded to nearly 20,000 acres by Thursday (5)(6).

The Fairview fire led to very unhealthy air quality in Hemet, California on Thursday. Source: IQAir.

Another small Southern California city experienced poor air quality on Thursday. The 990-acre Radford fire burned south of Big Bear Lake, where concentrations of PM2.5 measured from 46 to 88 µg/m3 (7).

Big Bear Lake, California, experienced unhealthy air quality as smoke from the Radford fire drifted into the city. Source: IQAir.

The Rodgers and Red fires in Yosemite National Park also contributed to overall poor air quality in central and northern California, as those largely uncontrolled fires still ranged from 2,540 to 6,056 acres respectively (8)(9).

Hazardous wildfire smoke in Montana and Idaho

Numerous small to medium wildfires in Idaho and Montana contributed to unhealthy and hazardous air quality found in those states on Thursday.

Cities most affected included Billings and Butte in Montana and Salmon, Idaho. Wildfire smoke in Billings resulted in PM2.5 concentrations in the very unhealthy range, 179 µg/m3.

Idaho wildfire smoke harmed air quality in both Idaho and Montana on Thursday. Source: IQAir.

Cascades' wildfire smoke chokes mountain towns

Wildfire smoke in Washington state worsened over the week, as the 4,540-acre White River fire covered more wilderness (10). Air quality in Twisp, Winthrop, and neighboring Cascade mountain range neighborhoods ranged from unhealthy to hazardous.

Concentrations of PM2.5 measured in Winthrop peaked at 204 µg/m3 at 6 AM, Thursday.

Small town Washington state suffered hazardous air quality from a nearby wildfire. Source: IQAir.

The takeaway

Even after the heat wave fully abates, its effects will linger in the western U.S. Dried underbrush will remain vulnerable to lightning strikes, and intense, large-scale wildfires will take time to extinguish. Apart from the inherent danger of large-scale wildfires, more wildfire smoke will put people’s health at risk.

Wildfire smoke doesn’t stay put. Winds carry smoke far from its source, bringing pollutants into distant communities.

The best way to protect yourself is to stay informed about your local air quality conditions. Download an air quality app and install air quality monitors so you can be notified when air quality is unsafe. If air quality is unhealthy, close windows, avoid going outdoors, and run an air purifier suited for wildfire smoke.