Dissertation/Thesis Abstract

Mercury in the atmosphere: Measurements of particulate and gaseous forms in several different ecosystems
by Feddersen, Dara Marina, Ph.D., University of New Hampshire, 2013, 108; 3579690
Abstract (Summary)

Mercury (Hg) can exist in the atmosphere as gaseous elemental (Hg 0), reactive gaseous (RGM), and particulate bound mercury (Hg P) with active study including distribution, seasonality, and chemical transformations. Over one year, HgP data was collected using bulk filters, cascade impactors and the Tekran automated speciation unit at a marine site (Appledore Island) and a coastal site (Thompson Farm). This allowed for comparison of size distribution, seasonality, and methods of detection. During summer 2009, HgP was found (50-60%) in coarse fractions composed of sea salt particles at both sites. In winter, HgP was dominated (65%) by fine particles, while in spring and summer 2010, Hg P was distributed across coarse and fine fractions (40% each). Hg" exhibited a diurnal cycle that matched Hg0. Finally, dry deposition rates of HgP were calculated as 1.7-2.8 ngm -2day-1 in summer, 4.6 ngm-2day -1 in winter, and 2.5 ngm-2day-1 in spring.

An instrument was developed for aircraft measurements of total gaseous mercury (TGM) and Hg0 and thus RGM by the difference. The custom-fabricated instrument (UH-Merc) allows for lower detection limits (5 ppqv), lower time resolution (1 minute), and increased accuracy and precision (<3% each) than commercial instruments. First results match data from the Tekran unit during an inter-comparison campaign in Reno, NV as well as previous results for this site. In addition, the instrument recovered 95.5 ± 1.8% of spiked Hg0. UH-Merc will improve measurements to get a better understanding of Hg in the atmosphere.

Finally, TGM was collected from a forest (Thompson Farm) and a wetland site (Sallie's Fen) where TGM and methane (CH4) stored over the winter was being released into the atmosphere during the thaw. Results showed an increase of 23-28 ppqv TGM in the spring at Thompson Farm and 25-80 ppqv TGM and an increased flux of ~200 mg CH4 m-2day -1 at Sallie's Fen. The different processes forming these TGM and CH4 in the atmosphere become dominant as summer progresses; TGM decreases, while methane increases to a fall maximum. TGM seasonal and diurnal patterns are similar at Thompson Farm and Sallie's Fen; however, TGM is amplified up to 20% at Sallie's Fen.

Indexing (document details)
Advisor: Talbot, Robert
School: University of New Hampshire
School Location: United States -- New Hampshire
Source: DAI-B 75/06(E), Dissertation Abstracts International
Subjects: Atmospheric Chemistry, Chemistry
Keywords: Aircraft, Climate change, Mercury, Size distribution, Wetland
Publication Number: 3579690
ISBN: 978-1-303-79008-9
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