Year-round records of bulk and size-segregated aerosol composition and HCl and HNO3 levels in the Dumont d'Urville (coastal Antarctica) atmosphere:: Implications for sea-salt aerosol fractionation in the winter and summer -: art. no. 4645

[1] Year-round composition of bulk and size-segregated aerosol was examined at a coastal Antarctic site (Dumont d'Urville). Sea-salt particles display a summer depletion of chloride relative to sodium, which reaches similar to10%. The mass chloride loss is maximum on 1- to 3-mum-diameter particles, nitrate being often the anion causing the chloride loss. The summer SO42-/Na+ ratio exceeds the seawater value on submicron particles due to biogenic sulfate and on coarse particles due to ornithogenic (guano-enriched soils) sulfate and to heterogeneous uptake of SO2 (or H2SO4). HCl levels range from 47 +/- 28 ng m(-3) in the winter to 130 +/- 110 ng m(-3) in the summer, being close to the mass chloride loss of sea- salt aerosols. In the winter, sea- salt particles exhibit Cl-/Na+ and SO42-/Na+ mass ratios of 1.9 +/- 0.1 and 0.13 +/- 0.04, respectively. Resulting from precipitation of mirabilite during freezing of seawater, this sulfate-depletion-relative sodium takes place from May to October. From March to April, warmer temperatures and/or smaller sea ice extent offshore the site limit the phenomenon. A range of 14-50 ng m(-3) of submicron sulfate is found, confirming the existence of nssSO(4)(2-) in the winter at a coastal Antarctic site, highest values being found in the winters of 1992-1994 due to the Pinatubo volcanic input. Apart from these three winters, nssSO(4)(2-) levels range between 15 and 30 ng m(-3), but its origin is still unclear (quasi-continuous SO2 emissions from the Mount Erebus volcano or local wintertime dimethyl sulfide [DMS] oxidation, in addition to long-range transported byproduct of DMS oxidation).