Siberian Biomass Burning Plumes Across the Pacific: Aircraft Observations in the Pacific Northwest

During the summer of 2003, we employed a small research aircraft to collect vertical profiles of O3, CO, and total aerosol scattering in the 0 to 6 km column along the northwestern coastline of Washington State. Surface observations were also made and are discussed in the presentation by Jaffe et al. We conducted nine research flights between May 27 and August 5 and frequently observed airmasses with highly correlated enhancements of O3, CO, and aerosol scattering, especially the flights on June 2nd and August 5th. The most polluted airmass was observed on June 2, when absolute levels of O3, CO, and the aerosol scattering coefficient (green) exceeded 100 ppbv, 200 ppbv, and 130 Mm-1, respectively. The Del(O3)/Del(CO) and Del(scattering)/Del(CO) values (0.40 ppbv/ppbv and 1.25 Mm-1/ ppbv, respectively) observed during this episode are similar to our previous observations of Asian boreal fire emissions transported to the Northeast Pacific during May 2002. Subsequent analyses of back-trajectories (NOAA Hysplit4), aerosol forecasting models (NAAPS/NOGAPS), and satellite images (NASA's TERRA MODIS/AQUA, TOMS) indicate that the June 2nd and August 5th events were primarily due to the long-range transport of Siberian boreal fire emissions. The summer of 2003 appears to be exceptional in terms of the amount of Siberian biomass burning. Our observations of the variability of background O3 in the 0-6 km column during the summer of 2003 are similar to O3-sonde data collected in Northern California from 1995 through 2002. These results suggest that transport of Siberian biomass burning emissions is an important component of the background O3 variability during summer along the west coast of the U.S.