Assessing the role of VSLS halocarbons in chemistry-climate interactions - a study using the UMUKCA-CheST model

We investigate the contributions of bromocarbons to the stratospheric bromine budget and their effect on ozone. We use the whole atmosphere (troposphere +stratosphere) chemistry-climate model UMUKCA-CheST with an improved halogen scheme and improved emission estimates of very short-lived substances (VSLS). Based on a pair of 20-year long integrations, we find that VSLS contribute ~5pptv of inorganic Br to the stratosphere, mainly from CHBr3 and CH2Br2. The ozone response to the increase of Br is complex due to climate-chemistry feedbacks. Significant ozone loss (up to 20%) in the lowermost stratosphere of the SH is modelled, which is likely due to the acceleration of heterogeneous reactions on polar stratospheric clouds (PSCs). This significant ozone reduction is also associating with air temperature drops (~2 degrees Celsius) and a reduction in age of air (~1 month). Compared to a model run without the VSLS emissions, the atmospheric column ozone is reduced by several Dobson Units (DUs) in low latitudes and up to tens DUs in mid-to-high latitudes. The ozone response to the VSLS changes can be attributed to the combined effect of chemistry and dynamics; the ozone change affects the radiative heating and alters the Brewer-Dobson circulation, which in turn affects chemistry and eventually results in a 'new' equilibrium of the climate system.