Comparison of Aerosol at Four Baseline Atmospheric Monitoring Stations

Particles were captured by electrostatic precipitators or impactors at atmospheric monitoring bases in Alaska, Hawaii, Tasmania and Antarctica, and examined by electron microscopy. Particle number and mass distributions for radii ≲0.06 μm were similar at all sites. The particles appeared to be composed mainly of sulfuric acid (Alaska and Hawaii) or ammonium sulfate (Tasmania and Antarctica). Those of larger size showed marked differences in concentration size distribution and composition at the four sites. Those in Alaska differed from the remainder in that more than half contained insoluble inclusions and almost all particles were coated with, or wholly composed of, sulfuric acid. The Tasmanian aerosol was dominated by sea salt for particles with r > 0.1 μm, and many but not all of the micron-sized particles had benzene-soluble or ether-soluble components. At all except the Tasmanian site a maximum occurred in the mass distribution curve at a radius of ∼0.3 μm, and it is suggested that this is due to a residual sea-salt component that has been chemically and physically altered. Sulfate loadings under ambient pressures and temperatures for particle radii between 0.03 and 1 μm only were 0.8 μg m−3 in Alaska during winter, 0.14 μg m−3 in Antarctica and 0.08 μg m−3, in Hawaii. Particle production mechanisms over the ocean were shown from Tasmanian experience to operate equally during the hours of daylight or darkness. The mechanism of production of the Arctic and Antarctic aerosols that best agreed with their properties involved a circulation cell commencing from the lower troposphere in the vicinity of the polar jet, providing uplift to the upper troposphere or lower stratosphere, slow poleward transfer, and subsidence to lower levels at high latitudes.