Smoke from fires in North America (grey colors) as observed on 7 August 2018. The colored circles and triangles show the air quality index (AQI) at EPA PM2.5 monitors. Graphic: EPA

Dr. Jeff Masters
8 August 2018

(Weather Underground) – Smoke from the raging fires in California has brought dangerously high levels of fine particulate pollution (PM2.5, particles less than 2.5 microns or 0.0001 inch in diameter) to portions of California, Oregon, and Nevada since late July, and wildfire smoke now covers more than half of the continental U.S. and much of Canada. Much of this smoke is due to the largest fire in California history, the Mendocino Complex, which had burned over 292,000 acres as of August 8, and was just 34% contained. A major amount of smoke has also come from the sixth deadliest fire in California history, the Carr fire, which has killed 7 people and burned over 172,000 acres, and is 47% contained. According to the National Interagency Fire Center, on August 8 there were 107 active large fires in the U.S., which had collectively burned over 1.6 million acres. […]

On three consecutive days, July 26 – 28, hourly levels of PM2.5 pollution in Yosemite peaked above a suffocating 400 μg/m3, thanks to smoke from the Ferguson fire. On August 3, a personal air pollution sensor made by recorded even higher levels of PM2.5 at Wawona, on the south side of the park: an insanely high 1044 μg/m3. There is no EPA 1-hour standard for PM2.5, but the 24-hour standard is 35 μg/m3, and PM2.5 levels in excess of 250 μg/m3 maintained for an entire day are considered “hazardous”—the highest level on the Air Quality Index (AQI) scale. The highest 24-hour PM2.5 levels in Yosemite were 166 μg/mon July 28, which is solidly in the purple “very unhealthy” range. At this level, EPA warns to expect “Significant aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; significant increase in respiratory effects in general population.” [more]

Wildfire Smoke Causing Hazardous Air Quality in Western U.S.



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