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

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)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017) and C 2 Cl 4 (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(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. Plain Language SummaryThe 1987 Montreal Protocol banned production for dispersive uses of major ozone-depleting gases, such as chlorofluorocarbons, due to their role in depletion of the stratospheric ozone layer. In consequence, the ozone layer is expected to recover in coming decades, as stratospheric chlorine from banned substances slowly declines. However, chlorinated very short lived substances (Cl-VSLS), not controlled by the Montreal Protocol, represent a small, but growing, source of atmospheric chlorine that could potentially slow ozone recovery. It is thus important that the magnitude of emissions of

Rapid increase in dichloromethane emissions from China inferred through atmospheric observations

“…Emissions have grown substantially, from 683 (541–825) Gg yr −1 (68% uncertainty) in 2011 to 1038 (826–1251) Gg yr −1 in 2019, sustaining the trend observed before 2016, albeit with a lower emission growth rate after 2017. This estimate shows a similar increase to recently published global emissions, derived using TOMCAT (a global 3D model) with measurement data from both the US National Oceanic and Atmospheric Administration (NOAA) and AGAGE (adjusted to the NOAA calibration scale) 21 , or derived using a 12-box model with measurement data from NOAA alone 1 . The different global emissions estimates agree within 1 s.d.…”

“…The significant increase in global emissions of CH 2 Cl 2 , from 637 (600−673) Gg yr −1 (1 s.d. uncertainty) in 2006 to 1171 (1126−1216) Gg yr −1 in 2017, was attributed to an increase in industrial emissions from Asia 21 . As emissions from East and South Asia can be rapidly transported to the stratosphere by convective systems, it is critical to quantify emissions from this region to help understand its growing impact on stratospheric ozone.…”

Aircraft‐Based Observations of Ozone‐Depleting Substances in the Upper Troposphere and Lower Stratosphere in and Above the Asian Summer Monsoon

“…CHCl 3 and CH 2 Cl 2 are usually coproduced industrially (McCulloch, 2017). CH 2 Cl 2 has an atmospheric lifetime of about 6 months and its global atmospheric abundances are believed to be at least 90% anthropogenic in origin in recent years (Claxton et al., 2020; Engel, Rigby et al., 2018b). It has a wide range of industrial applications in chemical and pharmaceutical processes and in the production of HFC‐32 (CH 2 F 2 ; McCulloch, 2017).…”

“…However, this rate of decrease is slowing down: from 11.8 ± 6.9 ppt Cl yr −1 during 2008–2012 to 4.4 ± 4.1 ppt Cl yr −1 during 2012–2016 (Engel, Rigby et al., 2018b). This is due, in part, to increasing mixing ratios of chlorinated VSLSs, in particular, in East and South‐East Asia (Claxton et al., 2020; Engel, Rigby et al., 2018b; Fang et al., 2019). This could undermine some of the progress made by the Montreal Protocol and its amendments and further offset the reduction in emissions and mixing ratios of long‐lived ODSs.…”

“…Its primary use is in the manufacture of vinyl chloride, the precursor to polyvinyl chloride, and other chlorinated solvents (Oram et al, 2017). It is likely that there are major source regions of these chlorinated VSLSs in China and India (Claxton et al, 2020;Fang et al, 2019;Oram et al, 2017;Say et al, 2019).…”