Particulate Mercury in Wildfires Observed at the Mount Bachelor Observatory from 2005- 2007
Abstract
The chemical cycling of mercury in the environment has a significant atmospheric component with three primary forms: elemental mercury (Hg0), reactive gaseous mercury (RGM), and particulate mercury (PHg). Hg0 is the predominant atmospheric form (>95%) with a lifetime of 0.5-1 year. RGM is an operationally defined fraction of mercury (presumed to be composed mostly of Hg(II) compounds) that is adsorbed on a KCl coated denuder. PHg is the mercury fraction bound to particles captured on a glass-fiber filter (0.2 μm). While RGM and PHg are a small fraction of the atmospheric mercury burden, the uptake of RGM onto aerosols (creating PHg) and into cloud droplets increases the deposition of mercury to the Earth's surface and potential exposure by humans. Using three years of speciated mercury data (2005-2007) from the Mount Bachelor Observatory (2.7 km asl) in Bend, OR, we have identified seven periods ranging from 1-21 days long during which there was significant correlation between particulate mercury, aerosol scattering coefficient, and CO. These periods were typically observed from late May to early June with a few as late as mid July. During these periods we further identified 15 individual "events" lasting 12-24 hours during which PHg and aerosol scattering coefficients were highly correlated and typically above their monthly means. These events were also associated with increased CO and decreased RGM concentrations. Based on water vapor, O3, and RGM measurements, the observed events were usually associated with upslope flow of boundary layer air or mixed boundary layer/free tropospheric air. Using a combination of observed air chemistry (e.g. GEM/CO ratios), five day air mass back-trajectories, and TERRA satellite data most of these episodes can be attributed to fires in California, Oregon, and Canada. At least one episode may have been transported from eastern Asia. The slopes of the PHg/?sp and PHg/CO relationships range from 0.20-1.57 pg/Mm-1 and 0.11-1.3 pg/ppb, respectively. The range of slopes may be indicative of different types of burning (e.g. flaming vs. smoldering), differing amounts of chemical processing, or different fuel sources. These slopes provide boundaries for the expected relationship between PHg, CO, and aerosol scatter from wildfires.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A53D0321F
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 0365 Troposphere: composition and chemistry