Tropical stratospheric Ozone ChangesFollowing the Eruption of Mount Pinatubo

Abstract

The June 1991 Mount Pinatubo eruption placed a large amt. of SO2 in the stratosphere which was converted to H2SO4 aerosols 2-3 mo after eruption. These aerosols remained primarily in the tropical stratospheric reservoir (TSR) for the first 6 mo or so after the eruption before being largely dispersed to mid-latitudes. The large amt. of SO2 and aerosols in the TSR was sufficient to cause easily observable changes in stratospheric O3. There was an initial 2% column increase caused by photooxidn. of SO2, followed by a 5% column decrease in the region from the equator to 10°S in August-Nov. 1991 based on total O3 mapping spectrometer (TOMS) data. A comparison of electrochem. concn. cell (ECC) sonde data at Brazzaville (4°S) and Ascension Island (8°S) with historical pre-Pinatubo stratospheric aerosol and gas expt. II (SAGE II) O3 data indicated an 8% column decrease at 16-28 km along with a 2% column increase at 28-32 km. The 16-28 km decrease is likely due primarily to a combination of aerosol heating and lofting of the assocd. air mass and aerosol effects on photolysis, with small contributions from heterogeneous chem. involving the aerosols. The increase above 28 km is primarily due to NO2 removal by the aerosols, permitting the photochem. prodn. of O3 to be more efficient. The phase change of the QBO from easterly to westerly was delayed by the rising motion of the aerosols by ∼10 mo, resulting in a ∼10-D.U. decrease of O3 for that period vs. what would have been the case without the delay. In addn., in mid-1992, there was another min. in stratospheric O3 in the equator-to-10°S region, beyond that expected from QBO effects, which is not explained. [on SciFinder(R)]