1. Global 3-D simulation of reactive bromine chemistry T. Canty, Q. Li, R.J. Salawitch Jet Propulsion Laboratory, Caltech, Pasadena CA Tim.Canty@jpl.nasa.gov T it le

2. Measurements of column BrO from GOME much higher than standard stratospheric modeled values What’s the problem? Tropospheric BrO ? Missing stratospheric BrO? due to Arctic BL spring bloom

3. Hypotheses Discrepancy resolved by global, ubiquitous, background level of ~2 ppt of tropospheric BrO ( Platt and Hönninger, Chemosphere, 2003 & references therein ) – But: Schofield et al. (JGR, 2004) report upper limit of 0.9 ppt for tropospheric BrO over Lauder, NZ Discrepancy may be resolved by: ~ 1 ppt of tropospheric BrO (perhaps consistent with UL of Schofield et al., JGR, 2004 ) ~ 8 ppt of stratospheric of Bry in the lowermost stratosphere ( Salawitch et al., GRL, 2005 ) Stratospheric bromine supplied by decomposition of VSL (very short lived) organics not considered in most global models as well as tropospheric BrO ( Salawitch et al., GRL, 2005 ) Excess bromine in UT and LS has important consequences for: – mid-latitude ozone trends ( Salawitch et al., GRL, 2005 ) – tropospheric ozone photochemistry ( Boucher et al., ACP, 2003; von Glasow et al., ACP, 2004; Lary, ACP, 2004 ) – polar ozone loss ( Salawitch and Canty, in preparation, 2005 ) – chemistry - climate coupling ( Carpenter and Liss, JGR, 2000 ; Hollwedel et al., ACP, 2004; Quack et al., GRL, 2004 )

4. Enhanced Arctic BL BrO GOME Satellite data: BrO Enhancements over Hudson Bay & Arctic ice shelf every spring BrO column abundances of ~4  10 13 cm -2 seen at NH mid-latitudes year round Unlikely spring bloom BrO supplies all of the global tropospheric background, but may contribute Chance, GRL 1998

5. Br y TROP = 0 pptBr y TROP = 8 ppt AER Model Time Slice: 47°N, March 1993 Implications for Stratospheric Ozone Photochemistry Enhanced Bromine:   lower stratospheric ozone depletion due to BrO+ClO cycle  BrO+HO 2 cycle becomes significant O 3 sink below 16 km, extending into upper troposphere (BrO+HO 2 does not drive O 3 depletion because VSL source is assumed constant over time) Salawitch et al., GRL 2005

6. Tropospheric ozone: – zonal mean  6 to 18% for a high-latitude VSL source – local  up to 40%, maxim. in SH free trop during summer (von Glasow et al., ACP, 2004) DMS: – DMS + BrO becomes significant sink – DMS to SO 2 conversion efficiency dramatically  (von Glasow et al., ACD, 2003) (Boucher et al., ACP, 2003) NOx: – BrONO 2 hydrolysis significant source of HNO 3 (Lary, ACP, 2004) Implications for Tropospheric Ozone Photochemistry

7. Macroalgeal Ocean Source VMR Surface Lifetime Main Loss (ppt) (days) Process CHBr 3 Bromoform 2.0 – 20 26J CH 2 Br 2 Dibromomethane 0.8 – 3.4120OH CH 2 BrCl Bromochloromethane 0.1 – 0.3150OH C 3 H 7 Br n-propyl bromide 0.1 – 1.0 13OH C 2 H 5 Br Ethyl bromide 0.0 – 2.0 48OH CHBr 2 Cl Dibromochloro- 0.1 – 0.5 69OH & J methane C 2 H 4 Br 2 Ethylene dibromide 0.1 – 1.0 84OH Possible VSL organic sources

8. LocationSurface Water (mean;median) pmol/L Atmosphere (mean;median) ppt Global near shore (<2 km from shore) 934; 94625; 3.3 Global shelf71.7; 405.4; 2.2 Global open ocean18.3; 16.61.9; 1.2 Global oceanRange 0.6 - 2770 Range 0.2 - 460 mostly Atlantic oceanmostly Pacific ocean Oceanic and atmospheric bromoform from Quack et al., JGR, 2003

9. Adding CHBr 3 to GEOS-Chem Create bromine_mod.f Add ocean source of bromoform 1.Determine shore, shelf, and open ocean 2.Create ocean bromoform “mask” GEOS-CHEM v7-01-01 GEOS-Strat 4º x 5º grid

10. Land Ocean Near Shore Coastal Shelf Open Ocean 300 m 2 km Low CHBr 3 Ocean graph High CHBr 3 Use U.S. Navy bathymetry measurements of ocean depth (5x5 min.) Use focean to determine near shore region Create a “mask” file of ocean bromoform

11. Adding CHBr 3 to GEOS-CHEM Create bromine_mod.f Add ocean source of bromoform 1.Determine shore, shelf, and open ocean 2.Create ocean bromoform “mask” Add bromoform chemistry 1.Photolysis 2.Reaction with OH

12. Bromoform Chemistry RO 2, NO CHBr 3 CBr 3 OH O2O2 HOOCBr 3 HO 2 OH hvhv OOCBr 3 OCBr 3 C(O)Br 2 O 2 NOOCBr 3 NO 2 , hv  hvhv C(O)Br 2 RO 2, HO 2 RO 2, NO CHBr 3 CHBr 2 hvhv O2O2 HOOCHBr 2 HO2 OH hvhv OOCHBr 2 OCHBr 2 C(O)HBr O 2 NOOCHBr 2 NO 2 , hv  hvhv C(O)HBr RO 2, HO 2  1/3 of the time   100 days  2/3 of the time   36 days “Fast J” Little or no kinetic studies  total  26 days Fig. 2-6, WMO 2003

13. PEM Tropics-A results Lat = 18ºS Lon = 145ºW Need to understand CHBr 3 as prerequisite for understanding BrO

14. PEM Tropics-A results Lat = 18ºS Lon = 145ºW “Perfect World Scenario” Woohoo! Everything compares well.

15. Lat = 18ºS Lon = 145ºW PEM Tropics-A results D’Oh! Model does not seem to be affected by the ocean source. “Real World Scenario”

16. Conclusions Evidence for global, ubiquitous ~1 to 2 ppt of tropospheric BrO Potential important consequences for tropospheric: – O 3 – DMS oxidation – HNO 3 production Tropospheric BrO likely supplied by VSL organics Have begun to examine link between tropospheric BrO and biogenic, VSL organics using the GEOS-CHEM model – much work remains!!!

17. Future work Determine why modeled CHBr 3 is so low – identify and remove bugs Implement full CHBr 3 chemistry: – agreement between measured and modeled CHBr 3 – how much BrO is supplied to UT/LS by CHBr 3 – fate of decomposition products: aerosol uptake, heterog rxns Incorporate other VSL species