Nitrogen and sulfur species in Antarctic aerosols at Mawson, Palmer Station, and Marsh (King George Island)

Abstract

High volume bulk aerosol samples were collected continuously at three Antarctic sites: Mawson (67.60° S, 62.50° E) from 20 February 1987 to 6 January 1992; Palmer Station (64.77° S, 64.06° W) from 3 April 1990 to 15 June 1991; and Marsh (62.18° S, 58.30° W) from 28 March 1990, to 1 May 1991. All samples were analyzed for Na⁺, SO ²⁻₄ , NO ⁻₃ , methanesulfonate (MSA), NH ⁺₄ ,²¹⁰Pb, and⁷Be. At Mawson for which we have a multiple year data set, the annual mean concentration of each species sometimes vary significantly from one year to the next: Na⁺, 68–151 ng m⁻³; NO ⁻₃ , 25–30 ng m⁻³; nss SO ²⁻₄ , 81–97 ng m⁻³; MSA, 19–28 ng m⁻³; NH ⁺₄ , 16–21 ng m⁻³;²¹⁰Pb, 0.75–0.86 fCi m⁻³. Results from multiple variable regression of non-sea-salt (nss) SO ²⁻₄ with MSA and NO ⁻₃ as the independent variables indicates that, at Mawson, the nss SO ²⁻₄ /MSA ratio resulting from the oxidation of dimethylsulfide (DMS) is 2.80±0.13, about 13% lower than our earlier estimate (3.22) that was based on 2.5 years of data. A similar analysis indicates that the ratio at Palmer is about 40% lower, 1.71±0.10, and more comparable to previous results over the southern oceans. These results when combined with previously published data suggest that the differences in the ratio may reflect a more rapid loss of MSA relative to nss SO ²⁻₄ during transport over Antarctica from the oceanic source region. The mean²¹⁰Pb concentrations at Palmer and Marsh and the mean NO ⁻₃ concentration at Palmer are about a factor of two lower than those at Mawson. The²¹⁰Pb distributions are consistent with a²¹⁰Pb minimum in the marine boundary layer in the region of 40°–60° S. These features and the similar seasonalities of NO ⁻₃ and²¹⁰Pb at Mawson support the conclusion that the primary source regions for NO ⁻₃ are continental. In contrast, the mean concentrations of MSA, nss SO ²⁻₄ , and NH ⁺₄ at Palmer are all higher than those at Mawson: MSA by a factor of 2; nss SO ²⁻₄ by 10%; and NH ⁺₄ by more than 50%. However, the factor differences exhibit substantial seasonal variability; the largest differences generally occur during the austral summer when the concentrations of most of the species are highest. NH ⁺₄ /(nss SO ²⁻₄ +MSA) equivalent ratios indicate that NH₃ neutralizes about 60% of the sulfur acids during December at both Mawson and Palmer, but only about 30% at Mawson during February and March.