Growth in the Stratospheric Loading of Chlorinated Very Short-Lived Substances: Recent Trends and Implications for Future Ozone
Abstract
Very short-lived species (VSLS) are an important source of stratospheric halogens and contribute to ozone loss, particularly in the lower stratosphere, where ozone perturbations are most climate-relevant (Hossaini et al., 2015a,b). Chlorine VSLS, such as dichloromethane (CH2Cl2), are primarily anthropogenic and their production is not controlled by the Montreal Protocol. Long-term surface measurements of CH2Cl2, the most abundant chlorine VSLS, show its atmospheric concentration has more than doubled in the last decade. Here, we used the TOMCAT/SLIMCAT chemical transport model to quantify (i) recent trends in the emission and stratospheric input of CH2Cl2, (ii) the impact of CH2Cl2 on present day ozone & (iii) the impact of continued CH2Cl2 growth on future ozone. Constrained by time-dependent surface CH2Cl2 measurements, our model shows the contribution of CH2Cl2 to stratospheric Cl doubled between 2005 (36 ppt Cl) and 2016 (72 ppt Cl). The model reproduces well high-altitude CH2Cl2 measurements from recent NASA ATTREX missions. Increases in the stratospheric input of CH2Cl2 are attributed to increasing industrial emissions. We estimate a 1 Tg CH2Cl2/yr source is required to sustain observed present day CH2Cl2 concentrations. By comparing a simulation with CH2Cl2 considered to one without, we show that CH2Cl2 presently accounts for up to 10% of lower stratospheric Cly. Inclusion of CH2Cl2 leads to a modest reduction of the model springtime Antarctic ozone column of up to 3%. Assuming CH2Cl2 concentrations continue to increase at their present rate, our forward simulations show CH2Cl2 could account for 20-30% of lower stratospheric Cly by 2050, as the contribution from long-lived chlorocarbons declines. We find that continued CH2Cl2 growth could significantly delay the return of Antarctic ozone to pre-1980 levels by more than a decade. In conclusion, sustained future CH2Cl2 growth could significantly offset some of the future benefits of the Montreal Protocol and add uncertainty to projections of ozone recovery. - Hossaini, R., et al. Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone, Nat. Geosci., 2015a. Hossaini, R., et al. Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol, Geophys. Res. Lett., 2015b.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A43A0175H
- Keywords:
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- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0340 Middle atmosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3362 Stratosphere/troposphere interactions;
- ATMOSPHERIC PROCESSES