Subarctic atmospheric aerosol composition: 1. Ambient aerosol characterization

Subarctic aerosol was sampled during July 2007 at the Abisko Research Station Stordalen field site operated by the Royal Swedish Academy of Sciences. Located in northern Sweden at 68 degrees latitude and 385 m above sea level (m asl), this site is classified as a semicontinuous permafrost mire. Number density, size distribution, cloud condensation nucleus properties, and chemical composition of the ambient aerosol were determined. Back trajectories showed that three distinct air masses were present over Stordalen during the sampling period. Aerosol properties changed and correlated with air mass origin to the south, northeast, or west, suggesting that particle source and transport were important factors. We observe that Arctic aerosol is not compositionally unlike that found in the free troposphere at midlatitudes. Internal mixtures of sulfates and organics, many on insoluble biomass burning and/or elemental carbon cores, dominate the number density of particles from similar to 200-to 2000-nm aerodynamic diameter. Mineral dust that had interacted with gas-phase species was observed in all air masses. Sea salt, due to the uptake of nitrate species and loss of chlorine, was the aerosol type that most varied chemically with air mass.