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 (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 semivolatile 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. ¿ 1998 American Geophysical Union