Publication Details (including relevant citation information):
Bein, K.J., Zhao, Y., Johnston, M.V., and A.S. Wexler (2008), Interactions between boreal wildfire
and urban emissions, Journal of Geophysical Research - Atmospheres, 113(D7), D07304,
A suite of particulate, gaseous and meteorological measurements during the Pittsburgh Supersite experiment were used to characterize the impact of the 2002 Quebec wildfires on pollutant concentrations and physical and chemical processes dominant in the region. Temporal trends in the number distribution of wildfire particles – isolated using Rapid Single-ultrafine-particle Mass Spectrometry data – combined with CO, NOx and O3 mixing ratios identified two separate periods (Periods I and II) when the measurement site was directly impacted by plumes of relatively unprocessed wildfire emissions; i.e. increases in primary ultrafine wildfire particles, CO and NOx concomitant with a decrease in O3 from intra-plume NOx titration. Carbonaceous particle number distributions predominantly associated with vehicular emissions, PM2.5 sulfate mass concentration and SO2 mixing ratio resolved individual components of local and regional sources. Single particle signatures indicated a period of intense atmospheric processing following Period II that caused rapid growth of the ultrafine mode due to simultaneous sulfate and secondary organic mass accumulation, resulting in significant changes to particle physical and chemical properties. Particle growth was concurrent with large increases in O3 and maxima in incoming solar radiation and ambient temperature and is posited to have occurred in-situ as the air mass, containing a mixture of urban and wildfire emissions, was advected past the site. In total, the current work demonstrates significant added severity for pollution episodes in an area already burdened by large anthropogenic emission rates due to the impact of the 2002 Quebec wildfires. High levels of atmospheric processing increased sulfate accumulation and SOA formation and brought PM2.5 mass concentrations close to, and O3 mixing ratios in excess of, the National Ambient Air Quality Standards. Projections of increasing wildfire activity under a warming climate may increase the frequency and severity of such events.
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