Transport of forest fire emissions from Alaska and the Yukon Territory to Nova Scotia during summer 2004

Emissions from forest fires in Alaska and the Yukon Territory were observed at Chebogue Point, Nova Scotia (43.7°N, 66.1°W), between 11 and 13 July 2004. Smoke aerosols were first detected in the free troposphere by a Raman lidar and extended up to 8 km altitude. The plume was not evident at the surface until the second day, when increases in CO, acetonitrile (CH₃CN), benzene, and aerosol mass concentrations were observed by in situ instrumentation. Enhancement ratios for each species relative to CO agreed with the range of values from other measurements of the same plume. The surface aerosols had an elevated black carbon fraction relative to both CO and organic matter, and the ratio of black to organic carbon was higher than what is typically observed in fresh smoke. The emissions were tracked back to Alaska and the Yukon Territory using aerosol optical depth measurements from the Aqua MODIS satellite instrument, and the transport was reconstructed using the GEOS-Chem and FLEXPART atmospheric models. The analysis suggests that aerosols were injected into the atmosphere in proportion to CO and that aerosol removal processes were weak during the 7 to 9 day transit time in the free troposphere. Transport of the tracers to the ground was strongly connected to synoptic-scale features in the surface meteorology.