Size distribution of particulate mercury in marine and coastal atmospheres

Abstract. A study was conducted to determine the size distribution of particulate mercury (Hg^P) 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 Hg^P in ten size fractions ranging from > 10 μm to < 0.4 μm. During summer 2009, Hg^P 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, Hg^P at Thompson Farm was dominated (65%) by fine particles, while in spring and summer 2010, at both sites, Hg^P was distributed across the coarse and fine fractions (40% each). Using bulk filters to collect total Hg^P, we show a diurnal cycle that matches that of gaseous elemental mercury. Finally, dry deposition rates of Hg^P 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.