Contribution of Wildland-Fire Smoke to US PM_2.5 and Its Influence on Recent Trends

Abstract

Seasonal-mean concentrations of particulate matter with diameters smaller than 2.5 μm (PM 2.5 ) have been decreasing across the United States (US) for several decades, with large reductions in spring and summer in the eastern US. In contrast, summertime-mean PM 2.5 in the western US has not significantly decreased. Wildfires, a large source of summertime PM 2.5 in the western US, have been increasing in frequency and burned area in recent decades. Increases in extreme PM 2.5 events attributable to wildland fires have been observed in wildfire-prone regions, but it is unclear how these increases impact trends in seasonal-mean PM 2.5 . Using two distinct methods, (1) interpolated surface observations combined with satellite-based smoke plume estimates and (2) the GEOS-Chem chemical transport model (CTM), we identify recent trends (2006−2016) in summer smoke, nonsmoke, and total PM 2.5 across the US. We observe significant decreases in nonsmoke influenced PM 2.5 in the western US and find increases in summer-mean smoke PM 2.5 in fire-prone regions, although these are not statistically significant due to large interannual variability in the abundance of smoke. These results indicate that without the influence of wildland fires, we would expect to have observed improvements in summer fine particle pollution in the western US but likely weaker improvements than those observed in the eastern US.

A Decadal Climatology of Chemical, Physical, and Optical Properties of Ambient Smoke in the Western and Southeastern United States

“…Brey, Ruminski, et al (2018) andO'Dell et al (2019) demonstrate the usefulness of a satellite analysis product, the Hazard Mapping System Fire and Smoke Product (HMS), to identify the locations of smoke plumes and determine smoke impacted days and regions. Brey, Ruminski, et al (2018) andO'Dell et al (2019) demonstrate the usefulness of a satellite analysis product, the Hazard Mapping System Fire and Smoke Product (HMS), to identify the locations of smoke plumes and determine smoke impacted days and regions.…”

“…Brey, Ruminski, et al (2018) andO'Dell et al (2019) demonstrate the usefulness of a satellite analysis product, the Hazard Mapping System Fire and Smoke Product (HMS), to identify the locations of smoke plumes and determine smoke impacted days and regions. In this study, we extend the methods of Brey, Ruminski, et al (2018) andO'Dell et al (2019) to locate smoke plumes and then isolate smoke properties using the differences in aerosol properties between days with and without smoke impacts over a full decade of observations. To create HMS smoke polygons, analysts rely on visible satellite images; thus, it may be difficult to distinguish between smoke and cloud or smoke and anthropogenic haze.…”

“…As atmospheric aerosols are generally impacted by multiple sources (e.g., dust, sea salt and anthropogenic emissions), isolating the contribution of individual sources to observed aerosol properties is challenging. Brey, Ruminski, et al (2018) andO'Dell et al (2019) demonstrate the usefulness of a satellite analysis product, the Hazard Mapping System Fire and Smoke Product (HMS), to identify the locations of smoke plumes and determine smoke impacted days and regions. We summarize the relevant characteristics of the HMS smoke product here.…”

“…In addition, another limitation is that the HMS product does not provide any information on the vertical distribution of smoke, just the horizontal extent of the plume. In this study, we extend the methods of Brey, Ruminski, et al (2018) andO'Dell et al (2019) to locate smoke plumes and then isolate smoke properties using the differences in aerosol properties between days with and without smoke impacts over a full decade of observations. We estimate smoke properties (chemical composition and optical properties) using columnar and surface in situ measurements, and we evaluate how these properties vary across the western and SE United States-regions heavily impacted by fires, and for which we hypothesize that smoke properties may differ due to differences in fuels, fire type, and meteorology.…”

Simulating Forest Fire Plume Dispersion, Chemistry, and Aerosol Formation Using SAM-ASP version 1.0

“…They determined that wildfires are causing the increase in PM2.5 at the 98th quantile in the Northwest which could offset anthropogenic reductions in the region. 25 O'Dell et al (2019) and Knorr et al, (2018) combined surface observations and satellite-based smoke plume estimates and the GEOS-Chem chemical transport model (CTM) to identify trends in summer time smoke, non-smoke, and total PM2.5 across the US. They estimated that future PM emissions from biomass burning may exceed anthropogenic emission levels, including in densely populated areas in the eastern Europe-Russia-central Asia region.…”