HR: 09:15h
AN: A41F-05    [Abstracts]
TI: Factors Influencing the Large-Scale Distribution of Hg(0) in the Mexico City Area and Over the North Pacific
AU: * Talbot, R
EM: robert.talbot@unh.edu
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space Climate Change Research Center, Durham, NH 03824, United States
AU: Mao, H
EM: hmao@typhoon.sr.unh.edu
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space Climate Change Research Center, Durham, NH 03824, United States
AU: Scheuer, E
EM: eric.scheuer@unh.edu
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space Climate Change Research Center, Durham, NH 03824, United States
AU: Dibb, J
EM: jack.dibb@unh.edu
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space Climate Change Research Center, Durham, NH 03824, United States
AU: Avery, M
EM: m.a.avery@larc.nasa.gov
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681, United States
AU: Browell, E
EM: e.v.browell@larc.nasa.gov
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681, United States
AU: Sachse, G
EM: g.w.sachse@larc.nasa.gov
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681, United States
AU: Vay, S
EM: s.a.vay@larc.nasa.gov
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681, United States
AU: Blake, D
EM: drblake@uci.edu
AF: University of California-Irvine, Department of Chemistry, Irvine, CA 92697, United States
AU: Huey, G
EM: greg.huey@eas.gatech.edu
AF: Georgia Institute of Technology, Department of Earth and Atmospheric Sciences, Atlanta, GA 30332, United States
AU: Fuelberg, H
EM: fuelberg@met.fsu.edu
AF: Florida State University, Department of Meteorology, Tallahassee, FL 32306, United States
AB: Gas-phase elemental mercury (Hg°) was measured aboard the NASA DC-8 aircraft during the NASA Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign in spring 2006. Flights were conducted around Mexico City and on two subsequent deployments over the North Pacific based out of Honolulu, Hawaii and Anchorage, Alaska. Data was obtained during March-May 2006 and covered 0.15-12 km altitude. The vertical distribution in all three study regions showed that Hg° exhibited a relatively constant mixing ratio centered around 100 ppqv. Highly concentrated pollution plumes emanating from Mexico City revealed that mixing ratios of Hg° as large as 500 ppqv were correlated with combustion tracers such as CO, but not SO₂ which is presumably released from coal burning, refineries, and volcanoes. Our analysis of Mexico City plumes indicated that widespread multi-source urban/industrial emissions may have a more important influence on Hg° than specific point sources. Over the Pacific, correlations with CO, CO₂, CH₄, and C₂Cl₄ were diffuse overall, but recognizable on flights out of Anchorage and Honolulu. In distinct plumes originating from the Asian continent the Hg° - CO relationship was better defined and yielded an average value of ~0.0050 ng Hg° m^-3/ppbv, in good agreement with previous findings. A prominent feature of the INTEX-B dataset was frequent total depletion of Hg° in the upper troposphere when stratospherically influenced air was encountered. When O₃ mixing ratios exceeded 300 ppbv, Hg° was rarely detected. It appears that in the tropopause and stratosphere Hg° is oxidized on the order of days followed by heterogeneous transformation to particulate mercury. Our data confirm efficient chemical cycling of Hg° in the tropopause region and show that it is strongly anti-correlated with O₃. These processes constitute an effective chemical sink for Hg° at the top of the troposphere, which may recycle mercury back to the gas phase as stratospheric aerosols are eventually dispersed into the troposphere. Ozone data obtained with the differential absorption lidar (DIAL) showed that the stratospheric impact on the tropospheric column was a common and pervasive feature on all flights out of Honolulu and Anchorage. Mixing of stratospheric air, containing little or no Hg°, with tropospheric air should effectively reduce the mixing ratio of Hg° in the free troposphere. We propose that this is likely a major factor driving large-scale seasonality in Hg° mixing ratios, especially at mid-latitudes, and an important process that should be incorporated into global chemical transport models.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting