A Synthesis Inversion to Constrain Global Emissions of Two Very Short Lived Chlorocarbons: Dichloromethane, and Perchloroethylene

Claxton, Tom and Hossaini, Ryan and Wilson, Chris and Montzka, Stephen A. and Chipperfield, Martyn P. and Wild, Oliver and Bednarz, Ewa and Carpenter, Lucy and Andrews, Stephen and Hackenberg, Sina and Mühle, Jens and Oram, David and Park, Sunyoung and Park, Mi-Kyung and Atlas, Elliot and Navarro, Maria and Schauffler, Sue and Sherry, David and Vollmer, Martin and Schuck, Tanja and Engel, Andreas and Krummel, Paul B. and Maione, Michela and Arduini, Jgor and Saito, Takuya and Yokouchi, Yoko and O'Doherty, Simon and Young, Dickon and Lunder, Chris (2020) A Synthesis Inversion to Constrain Global Emissions of Two Very Short Lived Chlorocarbons: Dichloromethane, and Perchloroethylene. Journal of Geophysical Research: Atmospheres, 125 (12): e2019JD031. ISSN 0747-7309

Abstract

Dichloromethane (CH2Cl2) and perchloroethylene (C2Cl4) are chlorinated Very Short‐Lived Substances (Cl‐VSLS) with anthropogenic sources. Recent studies highlight the increasing influence of such compounds, particularly CH2Cl2, on the stratospheric chlorine budget and therefore on ozone depletion. Here, a multi‐year global‐scale synthesis inversion was performed to optimise CH2Cl2 (2006‐2017) and C2Cl4 (2007‐2017) emissions. The approach combines long‐term surface observations from global monitoring networks, output from a three‐dimensional chemical transport model (TOMCAT), and novel bottom‐up information on prior industry emissions. Our posterior results show an increase in global CH2Cl2 emissions from 637 ±36 Gg yr‐1 in 2006 to 1171 ±45 Gg yr‐1 in 2017, with Asian emissions accounting for 68% and 89% of these totals, respectively. In absolute terms, Asian CH2Cl2 emissions increased annually by 51 Gg yr‐1 over the study period, while European and North American emissions declined, indicating a continental‐scale shift in emission distribution since the mid‐2000s. For C2Cl4, we estimate a decrease in global emissions from 141 ±14 Gg yr‐1 in 2007 to 106 ±12 Gg yr‐1 in 2017. The time‐varying posterior emissions offer significant improvements over the prior. Utilising the posterior emissions leads to modelled tropospheric CH2Cl2 and C2Cl4 abundances and trends in good agreement to those observed (including independent observations to the inversion). A shorter C2Cl4 lifetime, from including an uncertain Cl sink, leads to larger global C2Cl4 emissions by a factor of ~1.5, which in some places improves model‐measurement agreement. The sensitivity of our findings to assumptions in the inversion procedure, including CH2Cl2 oceanic emissions, is discussed.