The physicochemical structure of the Greenland summer aerosol and its relation to atmospheric processes

Abstract

Relationships between size‐resolved aerosol chemistry and various atmospheric processes were studied at Summit over the Greenland ice sheet. The Summit summer aerosol displayed an Aitken mode below 0.1 μm aerodynamic particle diameter, one or two modes in the accumulation size range (0.1–1 μm), and a supermicron mode. The Aitken mode contained little particulate mass (<5%) but accounted for most of the particle number concentration. The accumulation size range frequently had two overlapping modes with a minimum around 0.4 μm. A potential reason for this bimodality is fog processing which occurs frequently over the ice sheet during summer nights. Most of the particulate sulfate, ammonium, methane sulfonic acid (MSA), and dicarboxylic were found in the accumulation size range, where they displayed quite a similar modal structure, suggestive of an internal mixture of these compounds in submicron particles. The ratio of MSA to sulfate varied with particle size over the accumulation size range, so that different deposition pathways are likely to cause different MSA to sulfate ratios in the surface snow. Less than 20% of particulate sulfate and >95% of particulate nitrate were usually found in supermicrometer particles. It is likely that the supermicron sulfate and nitrate are produced when SO2 and HNO3 react with particles of mostly crustal origin. Supermicron sulfate centered at a somewhat smaller size (<2 μm) than nitrate (2–3 μm). The particulate phase contained only minor amounts of semi volatile acidic compounds, except when the ice sheet was impacted by apparent biomass burning plumes. These plumes are characterized by elevated levels of many low‐volatility compounds, and they may contain submicron ammonium nitrate and ammonium formate.