On the Regional and Seasonal Ozone Depletion Potential of Chlorinated Very Short‐Lived Substances

• Published in: Geophysical research letters 2019-05, Vol.46 (10), p.5489-5498
• Main Authors: Claxton, Tom, Hossaini, Ryan, Wild, Oliver, Chipperfield, Martyn P., Wilson, Chris
• Format: Article
• Language: English
• Subjects: Antarctic ozone; Antarctic ozone hole; Anthropogenic factors; Boundary layers; Chemical transport; Chlorination; Chlorine; Chlorine budget; Chlorofluorocarbons; Chloroform; Dependence; Depletion; Dichloroethane; Dichloromethane; Emission analysis; Emissions; Gases; Global ozone; Human influences; Industrial applications; Methyl chloride; Montreal Protocol; ODP; Organic chemistry; Ozone; Ozone depletion; Ozone hole; Ozone layer; Ozonosphere; Perchloroethylene; Pollution dispersion; Pollution transport; Seasons; Stratosphere; Tetrachloroethylene; Transport; Tropical environments; Troposphere; VSLS
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL081455

Chloroform (CHCl3), dichloromethane (CH2Cl2), perchloroethylene (C2Cl4), and 1,2‐dichloroethane (C2H4Cl2) are chlorinated Very Short‐Lived Substances (Cl‐VSLS) with a range of commercial/industrial applications. Recent studies highlight the increasing influence of Cl‐VSLS on the stratospheric chlorine budget and therefore their possible role in ozone depletion. Here we evaluate the ozone depletion potential (ODP) of these Cl‐VSLS using a three‐dimensional chemical transport model and investigate sensitivity to emission location/season. The seasonal dependence of the ODPs is small, but ODPs vary by a factor of 2–3 depending on the continent of emission: 0.0143–0.0264 (CHCl3), 0.0097–0.0208 (CH2Cl2), 0.0057–0.0198 (C2Cl4), and 0.0029–0.0119 (C2H4Cl2). Asian emissions produce the largest ODPs owing to proximity to the tropics and efficient troposphere‐to‐stratosphere transport of air originating from industrialized East Asia. The Cl‐VSLS ODPs are generally small, but the upper ends of the CHCl3 and CH2Cl2 ranges are comparable to the mean ODP of methyl chloride (0.02), a longer‐lived ozone‐depleting substance. Plain Language Summary Anthropogenic emissions of long‐lived chlorinated substances (e.g., chlorofluorocarbons) have led to global ozone layer depletion since the 1970s/1980s, including the Antarctic Ozone Hole phenomenon. The 1987 Montreal Protocol was enacted to ban production of major ozone‐depleting gases, and in consequence, there are signs that the ozone layer is recovering. However, emissions of so‐called very short‐lived substances, such as dichloromethane, have increased in recent years. Historically, these compounds have not been considered a major threat to stratospheric ozone, due to relatively short lifetimes, and they are not controlled by the Protocol. Given that production of these compounds is projected to increase, it is important to determine their ability to affect stratospheric ozone. We quantify the ozone depletion potential (ODP) of chloroform and perchloroethylene and, for the first time, dichloromethane and 1,2‐dichloroethane, the main chlorinated very short‐lived substances. We show that their ODPs vary depending on where the emission occurs. For example, the ODP from Asian dichloromethane emissions is up to a factor of two greater than that from European emissions. This reflects the relative efficiency of troposphere to stratosphere transport between different geographical areas; the transport of polluted boundary layer air fr