Gaseous elemental and reactive mercury in Southern New Hampshire

Abstract. We conducted measurements of Hg⁰ and RGM at two inland sites, Thompson Farm (TF) and Pac Monadnock (PM), and a marine site (Appledore Island (AI)) from the UNH AIRMAP observing network in New Hampshire in 2007. Measurements of other important trace gases and meteorological variables were used to help understand influences on the atmospheric Hg budget in New England. Seasonal variation in both species observed at TF and PM is attributable to such factors as seasonal variation in deposition strength, meteorological conditions and biogenic emissions. Hg⁰ and RGM varied diurnally at TF, particularly in spring, following the trend in air temperature and jNO₂ and suggesting photochemical production of RGM. The diurnal patterns of Hg⁰ and RGM at AI during summer were nearly opposite in phase, with Hg⁰ decreasing through late afternoon, suggesting more significant photochemical oxidation of Hg⁰ to RGM in the marine environment, likely due to the presence of marine halogen compounds. A significant relationship of RGM with SO₂ at TF suggests a strong contribution of RGM from anthropogenic sources. Significant levels of halogen compounds measured at TF in previous studies, as well as similar Hg⁰ levels and Hg⁰-CO ratios at TF and AI may suggest that similar air masses are prevalent at these sites.