Joel Thornton and Theran Riedel Department of Atmospheric Sciences Department of Chemistry

1. On the relationship between nitryl chloride (ClNO2) and molecular chlorine (Cl2) in coastal California Joel Thornton and Theran Riedel Department of Atmospheric Sciences Department of Chemistry University of Washington Seattle, WA

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

3. Cl2 (molecular chlorine) HOCl + Cl-(aq) + H+(aq)  Cl2(g) + H2O BrCl + Cl-(aq)  Cl2 + Br-(aq) ClNO2 (nitryl chloride) N2O5 + Cl-(aq)  ClNO2(g) + HNO3 ClNO2 conversion to Cl2 ClNO2 + Cl-(aq) + H+(aq)  Cl2(g) + HONO Sources and Coupling Between ClNO2 and Cl2

4. What is Cl-X in Remote Regions? O3 CH4 HO2 ClO Cl HCl OH HOCl HOCl(aq) + H+ + Cl- Cl2(g) + H2O HOCl(aq) + H+ + Br- BrCl(g) + H2O HOBr(aq) + H+ + Cl-  BrCl(g) + H2O “autocatalytic mechanism” (greatly simplified here) Vogt, et al Nature 1996 Platt, et al ACP 2004

5. Cl NO2 Chlorine Activation by N2O5 2HNO3 H2O N2O5 NO2 + NO3 Cl- HNO3 + ClNO2 Finlayson-Pitts, Nature 1989 Behnke, et al JGR 1997

6. UW-Chemical Ionization Mass Spectrometer CDC CH3I/ N2 Quadrupole I- + ClNO2 I-ClNO2- electron multiplier I- + Cl2 I-Cl2- IMR I- + N2O5 I-N2O5- McNeill, et al Atmos. Chem. Phys. 2006 Kercher, et al Atmos. Meas. Tech. 2009 Octupole V. Faye McNeill (now Assist. Prof. Columbia University) James P. Kercher (now Assist. Prof Hiram College) Theran P. Riedel (UW Graduate Student)

7. Expected ClNO2 production Annual ClNO2 Production (g Cl/yr): Log color scale From: Thornton, et al. Nature 2010

8. ClNO2 pptv 2000 1000 200 CalNex ClNO2 observations Los Angeles, CA

9. Atomic Chlorine • Atomic Cl has a large oxidizing potential (10-100x OH) • Cl atoms have potential to substantially affect O3, VOC, and Hg levels. • Cl atom sources are uncertain, but Cl2 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. Atomic chlorine production ? HOCl H+, Cl- Cl2 ClNO2 Cl- OH N2O5 Cl HCl BrCl H+, Cl- HOBr

11. Expected ClNO2 production ClNO2 Production: log(g Cl/year) From: Thornton, et al. Nature 464, 2010

12. CalNex observations Los Angeles, CA ClNO2 pptv

13. Expected Cl2 levels • Spicer et al. at Long Island, NY, June 1996. • Finley and Saltzman at La Jolla, CA, January 2006. From: Spicer et al. Nature 394, 1998. AND Finley and Saltzman. JGR 113, 2008.

14. CalNex observations

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

16. ClNO2 and Cl2 correlations UTC DOY

17. Cl atom production: ClNO2 vs. Cl2

18. Thoughts • Our observations consistent with substantial inland production of Cl atom precursors transported to marine environments along with continued production off shore. • ClNO2 should be considered a Cl atom precursor with at least similar importance to Cl2. • Measurements of N2O5 and aerosol composition, mixing, play important roles given the heterogeneous reaction mechanism at work.

19. Opportunities for Collaboration & Future Analyses • ClNO2 production efficiencies • ClNO2 yield predictions • Utilize HCl measurements • Hydrocarbon evidence of Cl atom chemistry • Utilize PTRMS and GC-FID VOC data • ClNO2 as a fraction of NOy • Box modeling Cl activation and Cl atom chemistry

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

21. Finley and Satlzman. JGR 113, 2008