A Synthesis Inversion to Constrain Global Emissions of Two Very Short Lived Chlorocarbons: Dichloromethane, and Perchloroethylene
Tom Claxton, Ryan Hossaini, Chris Wilson, S. A. Montzka, Martyn P. Chipperfield, Oliver Wild, Ewa Bednarz, Lucy J. Carpenter, Stephen Andrews, S. C. Hackenberg, Jens Mühle, D. E. Oram, Sunyoung Park, Mi‐Kyung Park, E. Atlas, María Amparo Gilabert Navarro, S. Schauffler, David F. Sherry, Martin K. Vollmer, Tanja Schuck, Andreas Engel, Paul B. Krummel, Michela Maione, Jgor Arduini, Takuya Saito, Yoko Yokouchi, Simon O’Doherty, Dickon Young, Chris Lunder
Abstract
Abstract Dichloromethane (CH 2 Cl 2 ) and perchloroethylene (C 2 Cl 4 ) are chlorinated very short lived substances (Cl‐VSLS) with anthropogenic sources. Recent studies highlight the increasing influence of such compounds, particularly CH 2 Cl 2 , on the stratospheric chlorine budget and therefore on ozone depletion. Here, a multiyear global‐scale synthesis inversion was performed to optimize CH 2 Cl 2 (2006–2017) and C 2 Cl 4 (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 CH 2 Cl 2 emissions from 637 ± 36 Gg yr −1 in 2006 to 1,171 ± 45 Gg yr −1 in 2017, with Asian emissions accounting for 68% and 89% of these totals, respectively. In absolute terms, Asian CH 2 Cl 2 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 C 2 Cl 4 , 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. Utilizing the posterior emissions leads to modeled tropospheric CH 2 Cl 2 and C 2 Cl 4 abundances and trends in good agreement to those observed (including independent observations to the inversion). A shorter C 2 Cl 4 lifetime, from including an uncertain Cl sink, leads to larger global C 2 Cl 4 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 CH 2 Cl 2 oceanic emissions, is discussed.