Chlorinated Very Short-Lived Substances: development + evaluation of gridded emissions for global models and on recent emission trends

Chlorinated Very Short-Lived Substances (Cl-VSLS) are now recognised as a significant source of inorganic chlorine in both the troposphere and stratosphere (e.g. Hossaini et al., 2016, 2019). The most abundant Cl-VSLS are dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4) and 1,2−dichloroethane (C2H4Cl2), all of which have significant – but poorly constrained – industrial sources. Global surface observations have shown that the tropospheric abundance of CH2Cl2 and CHCl3 has increased significantly in recent years. For instance, the global surface abundance of CH2Cl2 has more than doubled since the early 2000s and in 2018 was ~42 ppt. Despite this, there has been no recent attempt to create a consistent set of gridded Cl-VSLS emissions with which global models can use to study their impacts. Here, we describe and evaluate a new set of gridded time-varying global emissions of CH2Cl2, CHCl3, C2Cl4 and C2H4Cl2, informed by novel bottom-up industrial emission data. The performance of the emission inventories in the TOMCAT chemical transport model are assessed using data from both long-term surface monitoring networks and a range of tropospheric aircraft campaigns. We use the model to quantify regional variability in Cl-VSLS throughout the troposphere and outline further plans for a new model intercomparison effort to examine the impacts of VSLS in the troposphere and stratosphere.