Coarse and Fine Particulate Matter Components of Wildland Fire Smoke at Devils Postpile National Monument, California, USA

Fine (PM2.5) and coarse (PM10) particulate matter were monitored during the summer and fall of 2018 at Devils Postpile National Monument, California, USA. This remote site, located in the Sierra Nevada, was downwind of a number of wildland fires that were burning in California. The coarse (PM2.5-10) and the fine (PM2.5) fractions of the PM in the wildland fire smoke showed median PM2.5-10/PM2.5 ratios of .47 and 1.37 during periods with and without smoke, respectively. The concentrations at ground level were significantly (p < 0.001) higher during the periods with smoke for both the PM2.5-10 (10.3 µg m–3) and the PM2.5 (35.3 µg m–3), although the PM2.5 contributed most of the increase. These concentrations suggest that the fire size and intensity along with the distance and transport of smoke determine the exposure risk to humans. Current exposure estimates obtained via modeling and emission estimates may misrepresent ground-level concentrations due to a lack of understanding of the aerosol distribution in an aging wildland fire smoke plume.