Condensed nitrate, sulfate, and chloride in Antarctic stratospheric aerosols

During the 1987 Airborne Antarctic Ozone Experiment we estimated the NO₃, Cl, and SO₄ contents of stratospheric aerosols by testing for the presence of condensed nitric, sulfuric, and hydrochloric acid. In various segments of the ER-2 sample flights, aerosol particles were impacted on four 500-mm-diameter gold wires, strung across aluminum rings. The wires were pretreated to give results specific to certain physical and chemical aerosol properties. One wire was carbon coated and used for aerosol concentration and size analyses by scanning electron microscopy. Simultaneous X ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride, and silver nitrate to detect nitric, sulfuric, and hydrochloric acids, respectively, in the aerosols. Wires were exposed at a number of geographic locations at altitudes near 18 km. Immediately after collection, the acids were fixed as ammonium salts by exposing them in flight to NH₃. Results show that condensed nitrate is found below a threshold temperature of 193.6±3.0 K, generally encountered at latitudes exceeding 64°S. A negative correlation exists between condensed nitrate and ozone concentration. This is consistent with theories that postulate removal of gas-phase NO_y as a necessary step in allowing active chlorine-ozone reactions to occur. Condensed H₂SO₄ is present at concentrations between 0.2 and 0.9 parts per billion by mass. The mass of condensed HCl is estimated to be approximately 3% of the mass of sulfuric acid.