HR: 0800h
AN: A11C-0610    [Abstracts]
TI: Seasonal and Diurnal Variations of Hg(0) Over New England
AU: * Mao, H
EM: hmao@gust.sr.unh.edu
AF: University of New Hamsphire, CCRC,EOS,39 College Rd., Durham, NH 03824,
AU: Talbot, R
EM: robert.talbot@unh.edu
AF: University of New Hamsphire, CCRC,EOS,39 College Rd., Durham, NH 03824,
AU: Sigler, J
EM: jsigler@gust.sr.unh.edu
AF: University of New Hamsphire, CCRC,EOS,39 College Rd., Durham, NH 03824,
AU: Sive, B
EM: bcs@gust.sr.unh.edu
AF: University of New Hamsphire, CCRC,EOS,39 College Rd., Durham, NH 03824,
AU: Hegarty, J
EM: jhegarty@gust.sr.unh.edu
AF: University of New Hamsphire, CCRC,EOS,39 College Rd., Durham, NH 03824,
AB: Diurnal to interannual variability of Hg° over New England was investigated using multiple years of Hg° measurements at two inland sites, Thompson Farm (TF, 43.11° N, 70.95° W, 24 m, 25 km inland) and Pac Monadnock (PM, 42.86° N, 71.88° W, 700 m, 180 km inland), and one summer of measurements from a marine site, Appledore Island (AI, 42.97° N, 70.62° W, sea level), from the University of New Hampshire AIRMAP observing network. Possible sources were identified via a thorough examination of relationships between Hg° and a number of trace gases, e.g., CO, CO₂, CH₄, NO_y, NO, SO₂, and VOCs. The measurements of Hg„a at TF showed distinct seasonality with an annual maxima in late winter - early spring and a minima in early fall, with large day-to-day variation. A decreasing trend in the mixing ratio of Hg„a over the time period of March - September occurred at a rate of 0.5 - 0.6 ppqv d^-1 for all years except 2004 (0.3 ppqv d^-1). Measurements of Hg° at the elevated site PM exhibited much smaller daily and annual variation, particularly reflected in the slower warm season decline (relative to TF) of 0.2 and 0.3 ppqv d^-1 in 2005 and 2006 respectively. The AI data appeared to track the variation observed at TF albeit with much higher minima. Hg° was correlated most strongly with CO and NOy in winter suggesting that anthropogenic emissions were the primary source of Hg° . Applying the Hg° - CO relationship, we found that the seasonally averaged Hg° mixing ratio of ~160 ppqv at PM can be considered the regional background level. The positive Hg° -NOy correlation along the lower boundary of all data points indicated dry deposition as a stronger sink for Hg° than suggested by previous studies. We estimated a dry deposition velocity for Hg° of 0.17 - 0.20 cm s^-1, and a lifetime of ~11 days in the local PBL at TF. Correlation between Hg° and CHBr₃ at both TF and AI suggested a role of the oceanic source influencing the ambient levels of Hg° in the marine and coastal environments. It was also hypothesized that the overall significantly lower Hg° levels and steeper decreasing trend during the warm season at TF compared to those at PM may reflect the impact of marine halogen chemistry. The stronger decline in warm season Hg° during 2005 compared to 2004 may indicate that changes in precipitation played a role in mitigating evasion from the surface. Colder winter climate was found to be accompanied by higher levels of all anthropogenic tracers except Hg° , possibly a result of the predominant meridional flow that entrained fresh emissions during transport of the polluted Arctic air mass as it circulated over the eastern U.S. In contrast, little variation in Hg° indicates a homogeneous distribution of surface Hg° mixing ratios in winter and/or quick removal of mercury released from anthropogenic sources. During warmer winters the Hg° -CO slope value possibly reflects the ratio of Hg° loss relative to changes in CO more than their emission ratios.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting