Spatially interpolated non-smoke and smoke PM2.5 concentrations for the US from 2006-2024

Seasonal-mean concentrations of particulate matter with diameters smaller
than 2.5 μm (PM2.5) 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 PM2.5 in the western US has not
significantly decreased. Wildfires, a large source of summertime
PM2.5 in the western US, have been increasing in frequency and
burned area in recent decades. Increases in extreme PM2.5 events
attributable to wildland fires have been observed in wildfire-prone
regions, but it is unclear how these increases impact trends in
seasonal-mean PM2.5. 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 PM2.5 across the
US. We observe significant decreases in nonsmoke influenced
PM2.5 in the western US and find increases in summer-mean smoke
PM2.5 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.