The Effect of Iodine Chemistry on Ozone Trends in the Lower Stratosphere

Recent studies have documented significant downward trends in ozone levels in the lower stratosphere. Conversely, simulations with the existing CCMs (chemistry-climate models) indicate nearly zero ozone trend. This discrepancy highlights the need to improve numerical models to better match observational data. Including the iodine-cycle ozone destruction reactions can enhance the model’s ability to reproduce the observed ozone trends in the lower stratosphere over time.

The SOCOL (SOlar Climate Ozone Link) of AERv2.I version is utilized, which incorporates gas-phase and heterogeneous reactions involving atmospheric iodine compounds in the photochemical scheme, enabling consideration of the iodine cycle in ozone destruction. In this study, two model simulations of Earth’s atmospheric evolution from 1975 to 2020 were conducted. The first simulation did not include iodine emissions (the reference run or NO-I-EMIS), while in the second simulation accounted for iodine emissions (I-EMIS).

Overall, both numerical experiments show a significant increase in tropospheric ozone content and a decrease in the south polar region. The average trend values for the NO-I-EMIS and I-EMIS model runs are 1.12%/dec and 0.98%/dec, respectively. In the NO-I-EMIS experiment, the ozone trend at Northern midlatitudes in the lower stratosphere is negative (about -0.2%/dec) above 100 hPa and positive below 100 hPa. However, the area showing statistical significance is limited to a small region (25°-35° N). In the I-EMIS experiment, a more pronounced negative trend (around -0.5%/dec) was observed above the same height, with statistical significance over a broader region (10°-50° N).

This research was funded by Saint Petersburg State University under research project 124032000025-1.