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Speciated mercury at marine, coastal, and inland sites in New England – Part 1: Temporal variability

Author(s): H. Mao | R. Talbot

Journal: Atmospheric Chemistry and Physics Discussions
ISSN 1680-7367

Volume: 11;
Issue: 12;
Start page: 32301;
Date: 2011;
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A comprehensive analysis was conducted using long-term continuous measurements of gaseous elemental mercury (Hgo), reactive mercury (RGM), and particulate phase mercury (HgP) at coastal (Thompson Farm, denoted as TF), marine (Appledore Island, denoted as AI), and elevated inland (Pac Monadnock, denoted as PM) sites from the AIRMAP Observatories. Decreasing trends in background Hgo were identified in the 7- and 5-yr records at TF and PM with decline rates of 3.3 parts per quadrillion by volume (ppqv) yr−1 and 6.3 ppqv yr−1, respectively. Common characteristics at these sites were the reproducible annual cycle of Hgo with its maximum in winter-spring and minimum in fall as well as a decline/increase trend in the warm/cool season. The coastal site TF differed from the other two sites with its exceptionally low levels (as low as below 50 ppqv) in the nocturnal inversion layer probably due to dissolution in dew water. Year-to-year variability was observed in the warm season decline in Hgo at TF varying from a minimum total seasonal loss of 20 ppqv in 2010 to a maximum of 92 ppqv in 2005, whereas variability remained small at AI and PM. Measurements of Hgo at PM, an elevated inland rural site, exhibited the smallest diurnal to annual variability among the three environments, where peak levels rarely exceeded 250 ppqv and the minimum was typically 100 ppqv. It should be noted that summertime diurnal patterns at TF and AI are opposite in phase indicating strong sink(s) for Hgo during the day in the marine boundary layer, which is consistent with the hypothesis of Hgo oxidation by halogen radicals there. Mixing ratios of RGM in the coastal and marine boundary layers reached annual maximum in spring and minimum in fall, whereas at PM levels were generally below the limit of detection (LOD) except in spring. RGM levels at AI were higher than at TF and PM indicating a stronger source strength(s) in the marine environment. Mixing ratios of HgP at AI and TF were close in magnitude to RGM levels and were mostly below 1 ppqv. Diurnal variation in HgP was barely discernible at TF and AI in spring and summer with higher levels during the day and smaller but above the LOD at night.
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