Enrichment of calcium in sea spray aerosol in the Arctic summer atmosphere

Abstract

Significant calcium enrichment relative to seawater was observed in bulk and size-segregated aerosols in the marine atmospheric boundary layer over the Arctic Ocean in summer. The calcium enrichment factor generally increased with decreasing particle size (aerodynamic diameter) in the fine mode (particle size <1.8 μm), especially within the particle size ranges of 1.8 μm to 0.56 μm and 0.18 μm to 0.1 μm. Potassium was slightly enriched and showed a similar trend of enrichment in fine mode particles. No positive enrichment was observed for magnesium. Calcium bound to certain organic compounds and possibly calcareous debris from marine organisms may have contributed to the calcium enrichment in aerosols. Model results predict that observed calcium enrichments would increase hygroscopic growth in both coarse (10 μm and 5.6 μm) and fine (0.56 μm and 1 μm) aerosol particles. Possible alteration of this model result due to interactions with anions notwithstanding, increases in hygroscopic growth would be particularly important in the Arctic summer when sea-salts constitute the major fraction of aerosol dry mass. This study provides unique insights into ocean-atmosphere chemical interactions in the high-latitude Arctic Ocean.