Assessing boreal forest fire smoke aerosol impacts on U.S. air quality: A case study using multiple data sets

We synthesize multiple ground-based and satellite measurements to track the physical and chemical evolution of biomass burning smoke plumes transported from western Canada to the northeastern U.S. This multiple data set case study is an advantageous methodology compared with using individual or small groups of data sets, each with their own limitations. The case study analyzed is a Canadian boreal forest fire event on July 4, 2006 with carbonaceous aerosol smoke emission magnitudes comparable to those during the summer fire seasons of the previous decade. We track long-range transport of these aerosol plumes with data from space-borne remote sensing satellite instruments (MODIS, OMI, MISR, CALIOP lidar, AIRS) and ground-based in situ and remote aerosol observations (AERONET CIMEL sky/Sun photometer, MPLNET lidar, IMPROVE, EPA AirNow). Convective lofting elevated smoke emissions above the boundary layer into the free troposphere, where high speed winds aloft led to rapid, long-range transport. Aerosol layer subsidence occurred during transport due to a region of surface high pressure. Smoke aerosols reaching the boundary layer led to surface fine particulate matter (PM_2.5) enhancements accompanied by changes in aerosol composition as the plume mixed with anthropogenic aerosols over the northeastern U.S. The extensive coverage of this smoke plume over the northeastern U.S. affected regional air quality, with increases of 10-20 μg m^-3 PM_2.5 attributable to biomass burning smoke aerosols and EPA 24-hour PM_2.5 standard exceedances along the U.S. East Coast. Although each data set individually provides a limited view of the transport of smoke emissions, we demonstrate that a multi-data set approach results in a more comprehensive view of potential impacts due to long-range transport of smoke from a less extreme fire event. Our case study demonstrates that fires emit smoke aerosols that under certain meteorological conditions can degrade regional air quality 3000 km from the source region, with additional implications for aerosol radiative forcing and regional haze over the northeastern U.S.