1. 1 On the relationship between nitryl chloride (ClNO 2 ) and molecular chlorine (Cl 2 ) in coastal California Joel Thornton and Theran Riedel Department of Atmospheric Sciences Department of Chemistry University of Washington Seattle, WA

2. 2 Tropospheric Chlorine Cycling Cl Cl-Xactivation CxHyCxHyCxHyCxHy acid displacement Cl - HCl sea spray ~2,000 Tg Anthro. + ~5 Tg Graedel and Keene, GBC,1995 25-35 Tg* *From methane isotopes measured in remote SH MBL Platt, et al ACP 2004 Allan, et al JGR 2007

3. 3 Sources and Coupling Between ClNO 2 and Cl 2 Cl 2 (molecular chlorine) –HOCl + Cl - (aq) + H + (aq)  Cl 2 (g) + H 2 O –BrCl + Cl - (aq)  Cl 2 + Br - (aq) ClNO 2 (nitryl chloride) –N 2 O 5 + Cl - (aq)  ClNO 2 (g) + HNO 3 ClNO 2 conversion to Cl 2 –ClNO 2 + Cl - (aq) + H + (aq)  Cl 2 (g) + HONO

4. 4 What is Cl-X in Remote Regions? HOCl(aq) + H + + Cl -  Cl 2 (g) + H 2 O HOCl(aq) + H + + Br -  BrCl(g) + H 2 O HOBr(aq) + H + + Cl -  BrCl(g) + H 2 O Vogt, et al Nature 1996 Platt, et al ACP 2004 ClHClClO HOCl O3O3 CH 4 HO 2 “autocatalytic mechanism” (greatly simplified here) OH

5. 5 Cl NO 2 Chlorine Activation by N 2 O 5 N2O5N2O5 2HNO 3 HNO 3 + ClNO 2 Cl - H2OH2O Finlayson-Pitts, Nature 1989 Behnke, et al JGR 1997 NO 2 + NO 3

6. 6 UW-Chemical Ionization Mass Spectrometer CDC Octupole Quadrupole electron multiplier CH 3 I/ N 2 IMR I - + ClNO 2  I-ClNO 2 - I - + N 2 O 5  I-N 2 O 5 - McNeill, et al Atmos. Chem. Phys. 2006 Kercher, et al Atmos. Meas. Tech. 2009 V. Faye McNeill (now Assist. Prof. Columbia University) James P. Kercher (now Assist. Prof Hiram College) Theran P. Riedel (UW Graduate Student) I - + Cl 2  I-Cl 2 -

7. 7 Log color scale Annual ClNO 2 Production (g Cl/yr): Expected ClNO 2 production From: Thornton, et al. Nature 2010

8. 8 CalNex ClNO 2 observations Los Angeles, CA ClNO 2 pptv 2000 1000 200

9. 9 Atomic Chlorine Atomic Cl has a large oxidizing potential (10-100x OH) Cl atoms have potential to substantially affect O 3, VOC, and Hg levels. Cl atom sources are uncertain, but Cl 2 has typically been considered the major Cl atom source in polluted regions –Pechtl and von Glasow. GRL, 2007 –Knipping and Dabdub. ES&T, 2003 –Spicer et al. Nature 394, 1998.

10. 10 Cl ClNO 2 Cl - Atomic chlorine production Cl 2 N2O5N2O5 HOCl BrCl OH HCl HOBr H +, Cl - ?

11. 11 log(g Cl/year) ClNO 2 Production: From: Thornton, et al. Nature 464, 2010 Expected ClNO 2 production

12. 12 CalNex observations ClNO 2 pptv Los Angeles, CA

13. 13 Expected Cl 2 levels From: Spicer et al. Nature 394, 1998. AND Finley and Saltzman. JGR 113, 2008. Spicer et al. at Long Island, NY, June 1996. Finley and Saltzman at La Jolla, CA, January 2006.

14. 14 CalNex observations

15. 15 Inland production and plume transport/interception? Santa Monica Bay

16. 16 ClNO 2 and Cl 2 correlations UTC DOY

17. 17 Cl atom production: ClNO 2 vs. Cl 2

18. 18 Thoughts Our observations consistent with substantial inland production of Cl atom precursors transported to marine environments along with continued production off shore. ClNO 2 should be considered a Cl atom precursor with at least similar importance to Cl 2. Measurements of N 2 O 5 and aerosol composition, mixing, play important roles given the heterogeneous reaction mechanism at work.

19. 19 Opportunities for Collaboration & Future Analyses ClNO 2 production efficiencies ClNO 2 yield predictions –Utilize HCl measurements Hydrocarbon evidence of Cl atom chemistry –Utilize PTRMS and GC-FID VOC data ClNO 2 as a fraction of NOy Box modeling Cl activation and Cl atom chemistry

20. 20 The End Funding: NASA NESSF NNX-10AN48H,

21. 21 Finley and Satlzman. JGR 113, 2008