Individual particle analyses of arctic aerosol samples collected during AGASP-III

Airborne aerosol samples were collected during the third experiment of the Arctic Gas and Aerosol Sampling Program (AGASP-III), and the individual particles were analysed with electron microscopes and an X-ray energy spectrometer. The temporal and spatial variations of arctic aerosol physiochemical characteristics were studied relevant to the source, transport and transformation. Air trajectories arriving at the sampling sites generally provided useful information to interpret the aerosol chemistry. When the air masses passed over northern Russia, most of the aerosols were crustal dust, and approximately one-half of them were coated with sulfate. When the air masses were from northwestern Europe, solid particles, coated with sulfuric acid droplets and sulfate particles were the majority. These were probably formed by heterogeneous nucleation of H₂SO₄ followed by partial or complete neutralization. Oven open water, numerous large drops containing solid particles and cubic NaCl crystals were observed. However, over the frozen ocean, the drops and seasalt crystals were diminished. Instead, small sulfuric acid droplets, which were probably formed by homogeneous nucleation, were the principal aerosol species. At high altitudes (>5 km), pure sulfuric acid droplets and sulfuric acid drops with foreign nuclei were the dominant aerosols; however, alumina particles occasionally appeared in large quantities. Sulfate aerosols were omnipresent in the arctic stratosphere, troposphere and planetary boundary layer, whereas few nitrate-containing particles were found and then only in the boundary layer.