The Response of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo at Southern and Northern Midlatitudes

Abstract

Observations have shown that the mass of nitrogen dioxide decreased at both southern and northern midlatitudes in the year following the eruption of Mt. Pinatubo, indicating that the volcanic aerosol had enhanced nitrogen dioxide depletion via heterogeneous chemistry. In contrast, the observed ozone response showed a northern midlatitude decrease and a small southern midlatitude increase. Previous simulations that included an enhancement of heterogeneous chemistry by the volcanic aerosol but no other effect of this aerosol produce ozone decreases in both hemispheres, contrary to observations. The authors' simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and Southern Hemisphere extratropical downwelling. This enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer-Dobson circulation, increased Southern Hemisphere ozone via advection, counteracting the ozone depletion due to heterogeneous chemistry on the Pinatubo aerosol.

Can we explain the observed methane variability after the Mount Pinatubo eruption?

“…A slight increase in stratospheric O 3 was observed in 1991 in the southern mid-latitudes because of an increase in the strength of the Brewer-Dobson circulation due to stratospheric heating by Pinatubo aerosols (Aquila et al, 2013). the CH 4 sink of more than 5 mg m −2 month −1 is modelled in the northern tropics in the summers of 1993, 1994 and 1995. The decrease in temperature and water vapour following the eruption led to a decrease in both OH production and the rate of reaction between OH and CH 4 .…”

“…The quasi-biennial oscillation (QBO) in stratospheric winds caused an additional IAV of about 1 % (2 DU). In addition to these natural cycles, enhanced O 3 depletion occurred in 1992 to 1994 due to dynamical changes and heterogeneous chemistry associated with the presence of Pinatubo sulfate particles in the stratosphere (Telford et al, 2009;Aquila et al, 2013). This caused a 3.5 % (8 DU) decrease in stratospheric O 3 from 1991 to early 1993, with the largest perturbations observed at northern mid-latitudes.…”

Total ozone trends from 1979 to 2016 derived from five merged observational datasets – the emergence into ozone recovery

“…Significant ozone depletion was also observed in the NH following the El Chichón major volcanic eruption in 1982 (e.g., Hofmann and Solomon, 1989). A positive ozone response to the El Chichón is evident in the SH middle latitudes, most likely due to the specific circulation changes induced by this volcanic event (Schnadt Poberaj et al, 2011;Aquila et al, 2013;Dhomse et al, 2015). This is also believed to have caused an initial extratropical increase in SH extratropical total ozone during the first 6 months following the Pinatubo eruption.…”

“…While Mt. Pinatubo led to enhanced ozone depletion, the Southern Hemisphere (SH) extratropical total ozone rather increased as a result of a particular dynamics condition following the El Chichón event (Schnadt Poberaj et al, 2011;Aquila et al, 2013;Dhomse et al, 2015). For El Chichón, the stratospheric aerosol optical depth (SAOD) at 550 nm from Sato et al (1993) is used as the explanatory variable, while newer data from the WACCM model are used for the period after 1990 that is dominated by the Mt.…”

The decrease in mid-stratospheric tropical ozone since 1991

“…Pinatubo may alter the chemistry and dynamics of the stratosphere for extended periods. Aquila et al (2013) compared a reference model with a model which simulated the effect of the volcanic aerosols on both chemistry and dynamics. They calculated an increase in O 3 of ∼ 2 % at 10 hPa in the tropics slightly more than a year after the eruption, with no strong latitudinal variation.…”