Increases in tropospheric chlorine from dichloromethane, a gas not controlled by the Montreal Protocol. S.A. Montzka 1 , R. Hossaini 2 , B.D. Hall 1 , L. Hu 1,3 , B.R. Miller 1,3 , C. Siso 1,3 , J.W. Elkins 1 , M.P. Chipperfield 2 , A. Andrews 1 , C. Sweeney 1,2 1 NOAA/ESRL/GMD, Boulder, USA 2 School of Earth and Environment, University of Leeds, Leeds, UK 3 CIRES, Univ. of Colorado, Boulder, USA Acknowledgements: Many other NOAA/HATS and NOAA/CCGG group members... NOAA & cooperative site personnel Cooperative site partners from: Chinese Meteorological Administration (L. Zhou) CSIRO, Australia (The 3 Pauls) Environment Canada (D. Worthy) Harvard Univ. National Science Foundation SCRIPPS/Humboldt Univ. US Forest service Univ. of Bristol, U.K. Univ. of Colorado INSTAAR Univ. Wisconsin, Madison Weizmann Institute, Israel (D. Yakir) US Dept of Energy CARB LBNL (M. Fischer, S. Biraud) Support in part from NOAA Climate Program Office’s AC4 Program
NOAA HATS flask results for dichloromethane (CH 2 Cl 2 ) show large atmospheric increases in recent years: Carpenter, L., S. Reimann, et al., WMO Ozone Assessment, 2014 Leedham-Elvidge, E.C., et al., Atmos. Chem. Phys., 2015 Hossaini, R., et al., Nature Geosci., 2015 Hossaini, R., et al., Geophys. Res. Lett., 2015, in press. Why all the fuss? CH 2 Cl 2 : * is emitted primarily from anthropogenic activities: -solvent, cleaning agent, chemical reagent (HFC-32) ~800 Gg in 2012 (2 times Cl flux from F-12 or F-11 in the 1980s) * is a short-lived gas (~5 month mean lifetime; 1.5 month in summer) * ratio of [upper troposphere (TTL)] / [boundary layer] ~80% but is NOT controlled by the Montreal Protocol For today: 1) how robust are changes observed for a short-lived gas? 2) how significant are changes for tropospheric chlorine? 3) where are the increased emissions coming from?
The NOAA Halocarbon Sampling Network: • • ALT • SUM • low alt. BRW • high alt. MHD • LEF Daily • • WLG • THD • HFM • WIS • Bi-wkly NWR • (Aircraft) • MLO KUM • SMO • CGO PSA • SPO •
1a) How robust are the observed changes? • 80 140 At “remote” sites: • ALT CH 2 Cl 2 • SUM • increases everywhere low alt 70 BRW flask record 120 • high alt. MHD • spo spo Dichloromethane (CH 2 Cl 2 , ppt) Dichloromethane (CH 2 Cl 2 , ppt) cgo LEF • • 60 NWR daily cgo smo • WLG • 100 THD smo • HFM psa • NH WIS psa mlo 50 sites mlo kum • • kum 80 MLO nwr nwr brw 40 KUM brw alt alt 60 mhd lef thd 30 hfm • sum mhd NH 40 SMO thd 20 Globe sum SH • 20 10 CGO SH sites 0 0 PSA • 1995 2000 2005 2010 2015 1995 2000 2005 2010 2015 SPO •
1a) How robust are the observed changes? • 140 At “remote” sites: • ALT CH 2 Cl 2 • SUM • increases everywhere low alt BRW flask record 120 • At some US sites: high alt. MHD • spo different trends… Dichloromethane (CH 2 Cl 2 , ppt) LEF • • NWR daily cgo • WLG • 100 THD smo • HFM • NH WIS psa sites mlo • • kum 80 MLO nwr KUM brw alt 60 lef hfm • mhd 40 SMO thd sum • 20 CGO SH sites 0 PSA • 1995 2000 2005 2010 2015 SPO •
1b) How consistent are trends for a short-lived gas? compare changes in ‘remote’ NH boundary layer to: a) free troposphere means above the U.S. b) results from the U.S. boundary layer Changes at 80 80 80 80 NH remote boundary layer sites remote surface NWR, LEF, THD only sites: Annual mean CH 2 Cl 2 (ppt) 70 70 70 70 Aircraft 30-45ºN (3±1, 5±1, 7±1 km asl) Aircraft 30-45ºN (1±1 km asl) ** are consistent 60 60 60 60 with those Towers, U.S. continent observed throughout the 50 50 50 50 troposphere ** are larger 40 40 40 40 than observed in the boundary 30 30 30 30 layer over the U.S. 20 20 20 20 NH remote bl sites: KUM, NWR, THD, 2004 2004 2004 2004 2006 2006 2006 2006 2008 2008 2008 2008 2010 2010 2010 2010 2012 2012 2012 2012 2014 2014 2014 2014 LEF, MHD, BRW, ALT Towers sites: AMT, BAO LEF, SCT, Year STR, WBI, WGC, WKT
2) How large is the chlorine increase from CH 2 Cl 2 ? * 80 pptCl in surface CH 2 Cl 2 means ~60 pptCl to the stratosphere a larger contribution than HCFC-141b or HCFC-142b * The rate of Cl increase from CH 2 Cl 2 : is comparable to the Cl increase from the sum of all HCFCs 40 Rate of Change Rate of change (ppt Chlorine/yr) 30 CFCs 20 HCFCs 10 0.8 * CH 2 Cl 2 0 CCl 4 -10 -20 Long-lived total -30 -40 CH 3 CCl 3 -50 1990 1995 2000 2005 2010 2015
3a) Which latitudes are driving the increase? The relative increase in annual mixing ratio by site: 2.6 CH 2 Cl 2 2.4 Comparable increases (as %) are observed Annual mean / 1998-2002 mean annual mean / 2008-2002 mean at all remote sites, even in the SH (blue) 2.2 spo The largest relative increase is observed cgo 2.0 at low- to mid-latitude NH sites smo psa 1.8 mlo 1.6 kum nwr 1.4 brw Normalized to alt 1.2 1998-2002 mhd thd 1.0 0.8 1996 2001 2006 2011 2016
3b) How have atmospheric distributions changed? Intrahemispheric gradients: NH: become smaller NH emissions shifting to lower latitudes SH: slightly larger Interhemispheric gradient: Constant over time! N vs S gradient set by time constants for loss and N – S exchange Arctic spo Northern 2.0 Hemisphere psa (by month, deseasonalized) cgo 1.5 Site / Global mean smo mlo kum 1.0 NH Tropics nwr brw 0.5 alt Southern sum Hemisphere NH 0.0 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015
Summary: In flask results for CH 2 Cl 2 since 1998-2002 we have observed: * consistent broad-scale changes in mole fractions (and seasonal variations) for a chemical with a 5-month global lifetime. Specifically: * about a factor of 2 increase at nearly all remote sites across the globe and consistent increases in the free troposphere above the U.S. * reduced mole fraction enhancements in the U.S. boundary layer These imply: * substantial increases in global emissions, but not from the U.S. (U.S. emissions are likely decreasing) Changes in the observed atmospheric distribution imply: * a substantial shift in emissions to lower latitudes of the Northern Hemisphere Finally : *stratospheric chlorine attributable to CH 2 Cl 2 is currently larger than contributed by either HCFC-141b or HCFC-142b and is increasing at a rate comparable to that from the sum of all HCFCs .
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