Where Do Aerosol Particles in the Antarctic Upper Troposphere Come from?

A Case Study in January 1983

Abstract

Elemental composition and features of individual aerosol particles collected on 25 January 1983 in the Antarctic upper troposphere of 7.2km altitude over Syowa Station (69°S) with use of an aircraft were examined by an electron microscope equipped with an energy-dispersive X-ray analyzer. Mineral-containing particles were dominant (74% by number) in aerosol particles of 0.1-1.6μm radius, indicating the global transport of particles from the eruption of El Chichon volcano (17°N) in April 1982. Modified sea-salt or halite particles were present in 6% of particles. Particles composed of only sulfate and/or sulfuric acid constituted in 15% and soot-like particles constituted 5%.
The transport routes of the mineral-containing particles were studied with the 3-dimensional trajectory analyses on the basis of the twice-daily U.S. NMC data. Although the back trajectories exhibit that majority of the air particles spread in the whole extratropical troposphere 20 days before, there are some air parcels (about 2%) which passed above 200mb in the Antarctic region. Since the mineral particle concentration in the stratosphere in January 1983 was very high, most aerosol particles of El Chichon origin collected in the Antarctic upper troposphere would be transported downward from the Antarctic stratosphere. If the modified sea-salt (or halite) particles collected in the Antarctic upper troposphere are of marine origin, the trajectory analysis shows that the particles must come from the subtropical ocean.
The present study also suggests that the main transport of aerosol particles from the stratosphere to the troposphere in summer occurs over Antarctica and the subtropical jet region. The Antarctic route is of primary importance for transport to the Antarctic upper troposphere. Moreover, it is expected that the transport from the mid-latitude troposphere to the Antarctic upper troposphere become important when the aerosol concentration in the stratosphere is lower than that in the troposphere. The results obtained in this study are also useful for the transport problems of other trace gases such as ozone and carbon dioxide.