HR: 09:45h
AN: A41D-08    [Abstracts]
TI: Measurements of Mercury Speciation in the Free Troposphere at the Mount Bachelor Observatory
AU: * Swartzendruber, P
EM: pswartz@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington , Seattle, WA 98195-1640
AU: * Swartzendruber, P
EM: pswartz@atmos.washington.edu
AF: Interdisciplinary Arts and Sciences, University of Washington, Bothell, WA 98011-8246
AU: Jaffe, D
EM: djaffe@u.washington.edu
AF: Interdisciplinary Arts and Sciences, University of Washington, Bothell, WA 98011-8246
AU: Prestbo, E
EM: ericp@frontiergeosciences.com
AF: Frontier Geosciences, 414 Pontius Ave N, Seattle, WA 98109
AU: Eckley Selin, N
EM: eckley@fas.harvard.edu
AF: Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138-2901
AU: Jacob, D
EM: djacob@fas.harvard.edu
AF: Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138-2901
AU: Park, R
EM: rjp@io.harvard.edu
AF: Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138-2901
AU: Jeagle, L
EM: jeagle@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington , Seattle, WA 98195-1640
AU: Strode, S
EM: sstrode@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington , Seattle, WA 98195-1640
AU: Smith, J
EM: smithje@u.washington.edu
AF: Interdisciplinary Arts and Sciences, University of Washington, Bothell, WA 98011-8246
AB: In the spring of 2005 we began continuous measurements of mercury speciation (GEM, RGM, and PHg) at the Mt. Bachelor Observatory (2.7km above sea level) in Oregon. We also measured a suite of complementary chemicals: CO, ozone, NOx, water vapor, aerosol scatter, CO₂, condensation nuclei, and radon, and have established that Mt. Bachelor frequently samples free tropospheric air under dry subsiding conditions. Measurements made from May-July found significant concentrations of RGM with a peak during the night (mean 54 pg/m³) and in dry subsiding air. We also found much lower concentrations of particulate bound Hg in the free troposphere. During episodes of RGM enhancement, total mercury (GEM + RGM + PHg) is relatively constant, GEM and water vapor are negatively correlated with ozone, and radon concentrations are low. Linear correlation and principle component (PCA) analysis reveals that RGM concentrations are unrelated to CO and aerosol scatter, which indicates that direct pollution effects do not explain the high concentrations seen at night. Instead, RGM is correlated with ozone and negatively correlated with water vapor, which suggests a source in the free troposphere. 5-day backtrajectories were run using the HYSPIT model and FNL data on non-cloudy evenings for the highest and lowest third of RGM concentrations (n=20,18 respectively). The low RGM trajectories generally originate from the lower troposphere and a majority (60%) have recently come from the planetary boundary layer. High RGM events generally originate in the middle and upper troposphere and there is a modest correlation between RGM concentration and time since the trajectory experienced rainfall (r² =0.43, p=0.0013). Assuming the modeled rainfall events are sufficient to scrub the air parcels of RGM, this suggests a free tropospheric lifetime for GEM against oxidation of about 20 days, which is significantly shorter than could be explained solely by a homogeneous reaction with ozone and has important implications for deposition. Finally, to better understand the sources and sinks of RGM, we will show a comparison of the observed concentrations with those predicted from the GEOS-CHEM global Hg model.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
DE: 0330 Geochemical cycles (1030)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005