Recent Trends in Stratospheric Chlorine From Very Short-Lived Substances
journal contributionposted on 2019-05-22, 15:50 authored by R Hossaini, E Atlas, SS Dhomse, MP Chipperfield, PF Bernath, AM Fernando, J Mühle, AA Leeson, SA Montzka, W Feng, JJ Harrison, P Krummel, MK Vollmer, S Reimann, S O'Doherty, D Young, M Maione, J Arduini, CR Lunder
Very short-lived substances (VSLS), including dichloromethane (CH 2 Cl 2 ), chloroform (CHCl 3 ), perchloroethylene (C 2 Cl 4 ), and 1,2-dichloroethane (C 2 H 4 Cl 2 ), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCl tot ) using a chemical transport model and atmospheric measurements, including novel high-altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCl tot increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases. The modeled evolution of chlorine source gas injection agrees well with historical aircraft data, which corroborate reported surface CH 2 Cl 2 increases since the mid-2000s. The relative contribution of VSLS to total stratospheric chlorine increased from ~2% in 2000 to ~3.4% in 2017, reflecting both VSLS growth and decreases in long-lived halocarbons. We derive a mean VSLCl tot growth rate of 3.8 (±0.3) ppt Cl/year between 2004 and 2017, though year-to-year growth rates are variable and were small or negative in the period 2015–2017. Whether this is a transient effect, or longer-term stabilization, requires monitoring. In the upper stratosphere, the modeled rate of HCl decline (2004–2017) is −5.2% per decade with VSLS included, in good agreement to ACE satellite data (−4.8% per decade), and 15% slower than a model simulation without VSLS. Thus, VSLS have offset a portion of stratospheric chlorine reductions since the mid-2000s.
This work was supported by RH's NERC Independent Research Fellowship (NE/N014375/1) and the NERC SISLAC project (NE/R001782/1). J.J.H. wishes to thank UKRI ‐ NERC for funding via the National Centre for Earth Observation, contract PR140015. The ACE mission is funded primarily by the Canadian Space Agency. ACE‐FTS data can be obtained from https://databace.scisat.ca/level2/ace_v3.5_v3.6/. AGAGE operations at Mace Head, Trinidad Head, Cape Matatula, Ragged Point, and Cape Grim are supported by the National Aeronautics and Space Administration (NASA) with grants NAG5‐12669, NNX07AE89G, NNX11AF17G, and NNX16AC98G to MIT, grants NNX07AE87G, NNX07AF09G, NNX11AF15G, and NNX11AF16G to SIO; by the Department for Business, Energy & Industrial Strategy (BEIS) contract 1028/06/2015 to the University of Bristol for Mace Head; by the National Oceanic and Atmospheric Administration (NOAA, USA) contract RA‐133‐R15‐CN‐0008 to the University of Bristol for Barbados; by the Commonwealth Scientific and Industrial Research Organization (CSIRO Australia), and the Bureau of Meteorology (Australia) for Cape Grim. The model simulations were performed on the national Archer and Leeds ARC HPC facilities.
CitationJournal of Geophysical Research: Atmospheres, 2019, 124(4) pp. 2318-2335
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
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