A growing threat to the ozone layer from short-lived anthropogenic chlorocarbons

Abstract

Abstract. Large and effective reductions in emissions of long-lived ozone-depleting substance (ODS) are being achieved through the Montreal Protocol, the effectiveness of which can be seen in the declining atmospheric abundances of many ODSs. An important remaining uncertainty concerns the role of very short-lived substances (VSLSs) which, owing to their relatively short atmospheric lifetimes (less than 6 months), are not regulated under the Montreal Protocol. Recent studies have found an unexplained increase in the global tropospheric abundance of one VSLS, dichloromethane (CH 2 Cl 2 ), which has increased by around 60 % over the past decade. Here we report dramatic enhancements of several chlorine-containing VSLSs (Cl-VSLSs), including CH 2 Cl 2 and CH 2 ClCH 2 Cl (1,2-dichloroethane), observed in surface and upper-tropospheric air in East and South East Asia. Surface observations were, on occasion, an order of magnitude higher than previously reported in the marine boundary layer, whilst upper-tropospheric data were up to 3 times higher than expected. In addition, we provide further evidence of an atmospheric transport mechanism whereby substantial amounts of industrial pollution from East Asia, including these chlorinated VSLSs, can rapidly, and regularly, be transported to tropical regions of the western Pacific and subsequently uplifted to the tropical upper troposphere. This latter region is a major provider of air entering the stratosphere, and so this mechanism, in conjunction with increasing emissions of Cl-VSLSs from East Asia, could potentially slow the expected recovery of stratospheric ozone.

Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery

“…Modelling studies imply that VSLSs preferentially destroy lower stratospheric ozone, though the effect outside of the polar latitudes is expected to be small (Hossaini et al, 2015. While VSLSs are thought to delay the recovery of the ozone layer, much uncertainty remains since observations and reaction rate kinetics are only available for some VSLSs (Oram et al, 2017). The uncertainties in model chemical boundary conditions, e.g.…”

Continued increase of CFC-113a (CCl<sub>3</sub>CF<sub>3</sub>) mixing ratios in the global atmosphere: emissions, occurrence and potential sources

“…Various pumps were used for the different sampling activities, all of which have been thoroughly tested for a large range of trace gases (Brenninkmeijer et al, 2007;Laube et al, 2010a;Allin et al, 2015 andOram et al, 2017). After collection, the samples were transported to the University of East Anglia (UEA) to be analysed on a high-sensitivity gas chromatograph coupled to a Waters AutoSpec magnetic sector mass spectrometer (GC-MS).…”

“…It came into force in 1989 and, other than for a few critical-use exceptions, there has been a global ban on CFC production since 2010 (UNEP, 2016a). Due to this, mixing ratios of most CFCs are now decreasing in the atmosphere, and the ozone hole shows signs of recovery (Pawson et al, 2014;Solomon et al, 2016). Continued reductions in CFC mixing ratios are needed to allow the ozone layer to recover to pre-1970 levels.…”

Chemical Characterisation of Water-soluble Ions in Atmospheric Particulate Matter on the East Coast of Peninsular Malaysia

“…Most of these air masses originated from the East China Sea and South China Sea and did not undergo 320 any significant continental influence. early February 2014 (Oram et al, 2017). A 7-day pollution or cold-surge event was reported between 19-01-2014 and 26-01-325 2014, when significantly enhanced concentrations of Cl-VSLSs were observed.…”

“…For example, whilst air masses arriving at Bachok from highly industrialised regions contained higher SO4 2-levels, the SO4 2-concentration remained above 5 µg m -3 throughout the entire measurement period. To further investigate the frequency and duration of the pollution or cold surge events, Oram et al performed a NAME trajectory 335 analysis using carbon monoxide (CO) as a tracer of industrial emissions from regions north of 20° N for 6 winter seasons (2009/2010 -2014/2015) (Oram et al, 2017). A strong correlation between CO and CH2Cl2 (a measured Cl-VSLS) was observed during the pollution episode in late January 2014.…”