How Badly Does Wildfire Affect Air Quality?


Two days before I took this picture, the Northern California wildfires began, sending smoky air over the Bay Area. On the third day, I ventured outside since the air felt okay to breathe but the hazy air still obscured the sun so much that it appeared red. I sat outside for ten to fifteen minutes and in that time, I could feel my eyes itching from the particles in the air.

Particulate matter is a known air quality concern, especially at the smallest sizes (less than 2.5 micrometers, termed PM 2.5) which can travel deepest into lungs. PM 2.5 arises from combustion so gas and diesel cars and some industry are major contributors of PM 2.5 pollution.

With the recent rush over protective face masks—and plenty of questions over the necessary level of mask—I wondered how the air quality during the wildfires compared with air quality on average. Human health risk is measured in one way by exposure over a period of time. Were there any locations in the U.S. with air quality worse than a few days of smoky air?

From the National Environmental Health Tracking Network, Sonoma County historically has an annual average concentration of PM 2.5 around 8 µg/m3. Readings from the Napa/Sonoma area during the wildfires were upwards of 200 µg/m3 and poor air quality lasted for a week or more. With 5 days of air quality of 200 µg/m3, the annual average is 2.7 µg/m3. Let’s assume the fires are in addition to average emissions. Do any U.S. locations have annual average air quality upwards of 11 µg/m3?

us air quality

In fact, quite a few places in the U.S. have annual average concentrations of PM 2.5 above 11 µg/m3. Despite the incredible amount of pollution contributed by the wildfires, other sources of pollution combined with weather patterns create greater regional particulate totals. As many recent articles have been quick to point out, the weekly highs during the wildfires are about the same as annual averages for air quality in Beijing, China, which makes air quality in the U.S. much healthier by comparison.

California has a wide range of air quality measurements. A closer look shows that air quality has improved vastly in several areas within the state in recent years, such as the Southern California counties of Los Angeles, San Bernardino, and Riverside. Wildfires and other one-off emission events seem to play little into overall air pollution since readings are consistently and significantly lower. Fortunately, and due to regulatory efforts, air quality is improving overall in the country in recent years. Spare the Air days in the Bay Area have at the very least brought awareness to air quality issues if not an immediate reduction in emissions.

ca air quality

Another way to look at air quality is by the number of people impacted by high particulate concentrations. While the counties of Fresno, Kern, Los Angeles, Riverside, San Diego, and Tulare all have high PM 2.5 readings, when it comes to the number of people affected, Los Angeles county has the highest impact historically, followed by its neighbors San Bernardino, Riverside, and Orange County. Los Angeles has had infamously bad air quality, but that is no longer true. While still topping the list in number of exceedances for days above the recommended particulate matter limit, the number of affected has dropped dramatically in the past decade despite population growth.

ca pm exceedance

It is true that exposure to air pollutants as a result of wildfire smoke is not greater than spending a year in some U.S. locations and other places around the world. As many news articles were quick to point out, the air quality at it’s worst during the Northern California wildfires was only slightly worse than average air quality in Beijing. Of course, with the means to prevent particle intake by wearing a respirator mask for a few days or weeks, avoidance of pollutant exposure as much as possible is best.

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