Abstract
Abstract. A study was conducted to determine the size distribution of particulate mercury (HgP) at a marine and coastal site, and to compare the seasonal variability at both sites. Data was collected during summer 2009 and 2010, winter 2010, and spring 2010. Two cascade impactors were used to collect HgP in ten size fractions ranging from > 10 μm to < 0.4 μm. During summer 2009, HgP was found mainly (50–60%) in coarse fractions, 1.1 to 5.8 μm, composed of sea salt particles at both our coastal site (Thompson Farm) and marine site (Appledore Island). In winter, HgP at Thompson Farm was dominated (65%) by fine particles, while in spring and summer 2010, at both sites, HgP was distributed across the coarse and fine fractions (40% each). Using bulk filters to collect total HgP, we show a diurnal cycle that matches that of gaseous elemental mercury. Finally, dry deposition rates of HgP were calculated to be 1.7–2.8 ng m−2 day−1 in the summer, 4.6 ng m−2 day−1 in the winter, and 2.5 ng m−2 day−1 in the spring.
Highlights
Understanding mercury transport and chemical transformations in the atmosphere is a key component to establishing its global cycle. Schroeder and Munthe (1998) summarized the physical, chemical and toxicological properties of atmospheric mercury, as well as various atmospheric pathways including anthropogenic and natural sources, aerial transport and distribution, chemical and physical transformations, and wet and dry deposition to the earth
The GEOS-Chem model indicates that anthropogenic US emissions account for 13–23 % of mercury deposition in the Northeast (Zhang et al.) and Driscoll et al (2007) suggest that most of that deposited mercury will reemit into the atmosphere
It is interesting to note that Appledore Island (Fig. 6a) had about twice as much total HgP than Thompson Farm, especially in the sea salt region of the size distribution possibly due to the involvement of halogen chemistry in Hg cycling in the marine boundary layer such that more RGM is produced which leads to more HgP (Holmes et al, 2009; Mao et al, 2008; Hedgecock and Pirrone, 2001; Sigler et al, 2009)
Summary
Understanding mercury transport and chemical transformations in the atmosphere is a key component to establishing its global cycle. Schroeder and Munthe (1998) summarized the physical, chemical and toxicological properties of atmospheric mercury, as well as various atmospheric pathways including anthropogenic and natural sources, aerial transport and distribution, chemical and physical transformations, and wet and dry deposition to the earth. Suburban sites have been well studied for size distribution of HgP, data from marine locations has not been published. The GEOS-Chem model indicates that anthropogenic US emissions account for 13–23 % of mercury deposition in the Northeast (Zhang et al.) and Driscoll et al (2007) suggest that most of that deposited mercury will reemit into the atmosphere At these sites, HgP is expected to dominate the fractions correlating to sea salt aerosols (1–6 μm) formed from bursting bubbles and waves breaking, which can affect areas up to 25 km from the coastline (De Leeuw et al, 2000; Athanasopoulou et al, 2008), dust particles, and/or ultrafine and accumulation particles (< 2 μm) emitted directly from combustion sources and resulting from coagulation of small particles (Finlayson-Pitts and Pitts, 2000)
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