Increases in tropospheric chlorine from dichloromethane, a gas not - - PowerPoint PPT Presentation

Increases in tropospheric chlorine from dichloromethane, a gas not controlled by the Montreal Protocol.

S.A. Montzka1, R. Hossaini2, B.D. Hall1, L. Hu1,3, B.R. Miller1,3, C. Siso1,3, J.W. Elkins1, M.P. Chipperfield2, A. Andrews1, C. Sweeney1,2

1 NOAA/ESRL/GMD, Boulder, USA 2 School of Earth and Environment, University of Leeds, Leeds, UK 3 CIRES, Univ. of Colorado, Boulder, USA

Support in part from NOAA Climate Program Office’s AC4 Program

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)

NOAA HATS flask results for dichloromethane (CH2Cl2) 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? CH2Cl2: * 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?

• ALT

BRW KUM SPO NWR MLO

• CGO

SMO

low alt. high alt.

• The NOAA Halocarbon Sampling Network:
• •
• PSA

WIS WLG MHD THD LEF HFM SUM

Bi-wkly

(Aircraft)

Daily

• ALT

BRW KUM SPO NWR MLO

• CGO

SMO

low alt high alt.

• 1a) How robust are the observed changes?
• •
• PSA

WIS WLG MHD THD LEF HFM SUM

daily

20 40 60 80 100 120 140 1995 2000 2005 2010 2015 Dichloromethane (CH2Cl2, ppt)

spo cgo smo psa mlo kum nwr brw alt lef hfm mhd thd sum

10 20 30 40 50 60 70 80 1995 2000 2005 2010 2015 Dichloromethane (CH2Cl2, ppt)

spo cgo smo psa mlo kum nwr brw alt mhd thd sum NH Globe SH

CH2Cl2 flask record

NH sites SH sites

At “remote” sites:  increases everywhere

• ALT

BRW KUM SPO NWR MLO

• CGO

SMO

low alt high alt.

• 1a) How robust are the observed changes?
• •
• PSA

WIS WLG MHD THD LEF HFM SUM

daily

20 40 60 80 100 120 140 1995 2000 2005 2010 2015 Dichloromethane (CH2Cl2, ppt)

spo cgo smo psa mlo kum nwr brw alt lef hfm mhd thd sum

CH2Cl2 flask record

NH sites SH sites

At “remote” sites:  increases everywhere At some US sites:  different trends…

20 30 40 50 60 70 80 2004 2006 2008 2010 2012 2014 20 30 40 50 60 70 80 2004 2006 2008 2010 2012 2014 20 30 40 50 60 70 80 2004 2006 2008 2010 2012 2014 20 30 40 50 60 70 80 2004 2006 2008 2010 2012 2014

Annual mean CH2Cl2 (ppt) Year NH remote boundary layer sites NWR, LEF, THD only Aircraft 30-45ºN (3±1, 5±1, 7±1 km asl) Aircraft 30-45ºN (1±1 km asl) Towers, U.S. continent

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

Towers sites: AMT, BAO LEF, SCT, STR, WBI, WGC, WKT NH remote bl sites: KUM, NWR, THD, LEF, MHD, BRW, ALT

Changes at remote surface sites:

** are consistent with those

• bserved

throughout the troposphere ** are larger than observed in the boundary layer over the U.S.

2) How large is the chlorine increase from CH2Cl2?

* 80 pptCl in surface CH2Cl2 means ~60 pptCl to the stratosphere  a larger contribution than HCFC-141b or HCFC-142b * The rate of Cl increase from CH2Cl2:  is comparable to the Cl increase from the sum of all HCFCs

• 50
• 40
• 30
• 20
• 10

10 20 30 40

1990 1995 2000 2005 2010 2015

Rate of change (ppt Chlorine/yr)

HCFCs Long-lived total CH3CCl3 CCl4 0.8 * CH2Cl2 CFCs

Rate of Change

3a) Which latitudes are driving the increase?

The relative increase in annual mixing ratio by site:

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

1996 2001 2006 2011 2016

annual mean / 2008-2002 mean

spo cgo smo psa mlo kum nwr brw alt mhd thd

CH2Cl2

Normalized to 1998-2002 The largest relative increase is observed at low- to mid-latitude NH sites Comparable increases (as %) are observed at all remote sites, even in the SH (blue) Annual mean / 1998-2002 mean

3b) How have atmospheric distributions changed? Intrahemispheric gradients: NH: become smaller SH: slightly larger Interhemispheric gradient: Constant over time!

Site / Global mean (by month, deseasonalized)

0.0 0.5 1.0 1.5 2.0

1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015

spo psa cgo smo mlo kum nwr brw alt sum NH Northern Hemisphere Southern Hemisphere Arctic NH Tropics

 NH emissions shifting to lower latitudes

N vs S gradient set by time constants for loss and N – S exchange



Summary:

In flask results for CH2Cl2 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 CH2Cl2 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.