Size distribution of particulate mercury in marine and coastal atmospheres

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.