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1. Title 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

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

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1013 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. Implications for Stratospheric Ozone Photochemistry AER Model Time Slice: 47°N, March 1993 BryTROP = 0 ppt BryTROP = 8 ppt Enhanced Bromine: lower stratospheric ozone depletion due to BrO+ClO cycle BrO+HO2 cycle becomes significant O3 sink below 16 km, extending into upper troposphere (BrO+HO2 does not drive O3 depletion because VSL source is assumed constant over time) Salawitch et al.,GRL 2005

6. Implications for Tropospheric Ozone Photochemistry • 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 SO2 conversion efficiency dramatically  (von Glasow et al., ACD, 2003) (Boucher et al., ACP, 2003) • NOx: – BrONO2 hydrolysis significant source of HNO3 (Lary, ACP, 2004)

7. Possible VSL organic sources Macroalgeal Ocean Source VMR Surface Lifetime Main Loss (ppt) (days) Process CHBr3 Bromoform 2.0 – 20 26 J CH2Br2 Dibromomethane 0.8 – 3.4 120 OH CH2BrCl Bromochloromethane 0.1 – 0.3 150 OH C3H7Br n-propyl bromide 0.1 – 1.0 13 OH C2H5Br Ethyl bromide 0.0 – 2.0 48 OH CHBr2Cl Dibromochloro- 0.1 – 0.5 69 OH & J methane C2H4Br2 Ethylene dibromide0.1 – 1.0 84 OH

8. Oceanic and atmospheric bromoform mostly Atlantic ocean mostly Pacific ocean from Quack et al., JGR, 2003

9. Adding CHBr3 to GEOS-Chem • GEOS-CHEM v7-01-01 • GEOS-Strat • 4º x 5º grid • Create bromine_mod.f • Add ocean source of bromoform • Determine shore, shelf, and open ocean • Create ocean bromoform “mask”

10. Ocean graph 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 Low CHBr3 High CHBr3 Near Shore Coastal Shelf Open Ocean 2 km 300 m Land Ocean

11. Adding CHBr3 to GEOS-CHEM • Create bromine_mod.f • Add ocean source of bromoform • Determine shore, shelf, and open ocean • Create ocean bromoform “mask” • Add bromoform chemistry • Photolysis • Reaction with OH

12. Bromoform Chemistry CHBr3 CHBr3 hv OH CHBr2 CBr3 O2 O2 OH OH RO2, HO2 RO2, HO2 C(O)HBr C(O)Br2 HOOCHBr2 HOOCBr3 HO2 HO2 , hv , hv O2NOOCHBr2 O2NOOCBr3 OOCBr3 OOCHBr2 hv hv NO2 NO2 RO2, NO RO2, NO hv hv OCHBr2 OCBr3   C(O)Br2 C(O)HBr 2/3 of the time   36 days “Fast J” 1/3 of the time   100 days 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 CHBr3 as prerequisite for understanding BrO

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

15. PEM Tropics-A results Lat = 18ºS Lon = 145ºW 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: • – O3 • – DMS oxidation • – HNO3 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 CHBr3 is so low • – identify and remove bugs • Implement full CHBr3 chemistry: • – agreement between measured and modeled CHBr3 • – how much BrO is supplied to UT/LS by CHBr3 • – fate of decomposition products: aerosol uptake, heterog rxns • Incorporate other VSL species