AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Long-range Transported North American Wildfire Aerosols Observed in Marine Boundary Layer of Eastern North Atlantic
Guangjie Zheng, Arthur J. Sedlacek, Allison Aiken, Yan Feng, Thomas Watson, Shira Raveh-Rubin, Janek Uin, Ernie R. Lewis, JIAN WANG, Washington University in St. Louis
Abstract Number: 649 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Biomass burning aerosols greatly impact climate by interacting with solar radiation and clouds, and wildfires are major sources of biomass burning aerosols. Compared to tropical grassland or Eurasia boreal forests, tree species in North America (NA) boreal forests can support high-intensity crown fires. The resulting stronger pyrocumulonimbus activities can inject NA wildfire aerosols to higher altitudes, where they can exert a stronger influence on Earth’s radiation balance and be spread over larger geographic areas. Moreover, frequency and intensity of NA wildfires have been greatly enhanced by global warming in recent decades, and are expected to further increase in the future.
Properties of aerosols from NA wildfires may vary substantially during their transport in the atmosphere, but this variation would be missed by most previous studies that were conducted in near-field. Here we present comprehensive characterization of climatically relevant properties of aged NA wildfire aerosols emitted from the record-breaking Canadian wildfires in August 2017. Despite the elevated injection height (13~20 km), these aerosols were transported downward into the marine boundary layer of eastern North Atlantic over a period of 10 days, owing to the dry intrusions in mid-latitude cyclones. The aged wildfire aerosols exhibited elevated single scattering albedos (0.93 to 0.96) at 529 nm, and low absorption Ångström exponents of less than 1 for 464 nm/648 nm pair, suggesting negligible brown carbon contribution and thick coatings. The hygroscopicity parameter, κ, ranged 0.2 to 0.4. Both aerosol size distribution and κ of the aged wildfire aerosol are similar with those previously reported in fresher wildfire plumes in NA free troposphere, suggesting minor changes in overall CCN activity during the long-range transport in free troposphere. However, the CCN activities differ substantially from those typically assumed in global climate models and those observed in south Africa, highlighting the need for more detailed model representation.