1. Widespread Halogen Activation by N 2 O 5 Heterogeneous Chemistry Joel Thornton Department of Atmospheric Sciences University of Washington, Seattle thornton@atmos.washington.edu J.P. Kercher, T.P. Riedel, N.L. Wagner, J. Cozic, J. Holloway, W.P. Dubé, G.M. Wolfe, P.K. Quinn, A.M. Middlebrook, B. Alexander, and S.S. Brown UW – NOAA ESRL and PMEL Collaboration

2. Tropospheric Chlorine Cycling Cl Cl-Xactivation CxHyCxHyCxHyCxHy acid displacement Cl - HCl sea spray ~10,000 Tg Anthro. + 3 – 5 Tg Graedel and Keene, GBC,1995 25-35 Tg* *From methane isotopes measured in remote SH MBL Platt, ACP 2004 Allan, JGR 2007

3. Chlorine Cycling: New Addition NO 3 NO 2 ClNO 2 N2O5N2O5 acid displacement pCl - Cl HCl activation CxHyCxHyCxHyCxHy 8 – 22 Tg Cl yr -1 Reference: Thornton, et al Nature 2010

4. ClNO 2 Production HX(s) HX(g) XNO 2 (s) + HNO 3 (s) References: Finlayson-Pitts et al. 1989; Behnke et al, 1989, 1992; Thornton and Abbatt, 2005; Bertram et al 2009; Raff et al 2009

5. Instantaneous ClNO 2 Yield References: Benkhe, et al JGR 1997; Roberts, et al GRL 2009; Bertram and Thornton, ACP 2009 N 2 O 5(aq) ClNO 2 + NO 3 - 2HNO 3 Cl - H2OH2O

6. Population Average Instantaneous ClNO 2 Yield References: Benkhe, et al JGR 1997; Roberts, et al GRL 2009; Bertram and Thornton, ACP 2009  (r p ) ~ 0.1  =1  =0 Surface Area Distribution Total Chlorine = pCl - + HCl(g) Cl - HCl(g) Equilibrium repartitioning

7. ClNO 2 as a Cl Atom Source Erickson et al 1996  0.06 Tg Cl yr -1 (MBL only) Osthoff et al 2008  3.2 Tg Cl yr -1 (Coastal and MBL only) “Bottom up” global Cl atom source from ClNO 2 “Top-down” global Cl atom source Allan, et al 2004  22 - 35 Tg Cl yr -1 Platt, et al 2004  ~ 35 Tg Cl yr -1 “Bottom up” local Cl atom source from ClNO 2 Pechtl and von Glasow: ClNO 2 < 50 ppt in Long Island Sound (during June)

8. 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 ~ 1-5 pptv in 1 second V. Faye McNeill (now at Columbia University) James P. Kercher (now at Hiram College) Theran P. Riedel (UW Graduate Student)

9. ClNO 2 in the Long Island Sound and Beyond log([ClNO 2 ]) 53W 57W63W71W 1500ppt Observed ClNO 2 is 2 – 20x greater than previous model predictions for Long Island Sound (e.g. Pechtl and von Glasow, GRL 2007) ClNO 2 production still evident in outflow 1 – 2 days downwind  ClNO2 ~0.5

10. Psuedo-Lagrangian Model Predictions ppbv NO 2 ppbv ClNO 2 or N 2 O 5 pptv

11. Fraction of NO x Reacting via N 2 O 5 WSp SuAu ~ 38% of NO x removed by N 2 O 5 over U.S. GEOS-Chem output from B. Alexander

13. (*Parking Lot behind ESRL’s David H. Skaags Building) ClNO 2 and N 2 O 5 in Boulder, CO* 37 Cl (cps) 35 Cl (cps)

14. Detailed Behavior of N 2 O 5 and ClNO 2

15. ACCRONIM February 11 - 25 2009 N 2 O 5 and ClNO 2 CO, O 3 NO, NO 2 Particle surface area Water-soluble particle composition Meteorology (RH, T, Winds) Kohler Mesa, Boulder, CO Reference: Thornton, et al Nature 2010

16. ACCRONIM Overview

17. Reactant and Product Relationships ClNO 2 and N 2 O 5 broadly correlated But relationship changes night- to-night and within a night

18. Total Chloride ClNO 2 routinely 4 – 10x greater than particulate Cl -, suggesting important role for HCl(g) Consistent with observationally constrained thermodynamic aerosol model

19. Chemical Box Modeling – 2 Examples

20. Chemical Modeling Example -2  ClNO2 over campaign ranged from ~ 7 – 36% February 22 nd -23 rd  ClNO2 ~0.18

21. IMPROVE NetworkNADP Network Is Boulder Special? fine mode m Cl /m total Aerosol Inorganics Model n Cl- /n NO3- n Cl- /(f N2O5 n NO3- )

22. IMPROVE NetworkNADP Network Is Boulder Special? Aerosol Inorganics Model Aerosol Chloride Based Yield Chloride moles per N 2 O 5 moles reacted

23. Estimating ClNO 2 Production over U.S. f N2O5  ClNO2 P ClNO2 =  ClNO2 f N2O5 E NOx Constrain with Observations GEOS-Chem EDGAR Database HNO 3 E NOx = L NOx NO x E NOx L NOx

24. Estimating ClNO 2 Production over U.S. Log(E NOx )  ClNO2 f N2O5 Log(P ClNO2 ) U.S. P ClNO2 = 1.4 - 3.5 Tg Cl yr -1

25. ClNO 2 and the Global Cl Atom Source Erickson et al  0.06 Tg Cl yr -1 Osthoff et al  3.2 Tg Cl yr -1 “Bottom up” global Cl atom source from ClNO 2 “Top-down” total global Cl atom source Allan, et al 2004  22 - 35 Tg Cl yr -1 Platt, et al 2004  ~ 35 Tg Cl yr -1 Our estimates  8 – 22 Tg Cl yr -1 MAP OF NO2

26. Chlorine Cycling: New Addition Anthropogenic NO x represents a large perturbation of Cl-atom budget Cl-atom source tied to our understanding of N 2 O 5 reactive uptake Nighttime chemistry not just a sink of O x – but a potential source NO 3 NO 2 ClNO 2 N2O5N2O5 acid displacement Cl - Cl HCl activation CxHyCxHyCxHyCxHy 8 – 22 Tg Cl yr -1

27. Implications: e.g. Wintertime Oxidants ClNO 2 = 600 pptv ClNO 2 = 350 pptv ClNO 2 = 0 pptv Figure 4 For 600 pptv ClNO 2 in February Cl + RH dominates HO x production (by >10x) from sunrise to 10AM Cl + RH leads to >30% more daytime HO x production

28. Some Outstanding Issues 1.Studies of wintertime nocturnal reactive nitrogen and morning HO x chemistry 2.HCl measurements are likely necessary to demonstrate “closure” between integrated L N2O5 and P ClNO2 3.ClNO 2 yields inferred from [N 2 O 5 ] and [ClNO 2 ] are often lower than predictions based on [pCl - ]  Chloride distribution? Phase? Losses of N 2 O 5 and/or ClNO 2 ? 4. Can we better validate/constrain f N2O5 ?

29. Where does the chloride in come from? Sea Spray Coal Burning Biomass/crop burning Biofuel Waste incineration (e.g. PVC) Playa dust Road salt (?) Cooling towers Swimming pools (?)… References: Graedel and Keene, 1995; Reff, et al, 2009

30. Kholer Mesa Often Above Nocturnal Surface Layer

31. Predicting Annual Average U.S. P ClNO2 Log(E NOx )  ClNO2 f N2O5 Log(P ClNO2 ) U.S. P ClNO2 = 1.4 - 3.5 Tg Cl yr -1

32. Measured Chloride Deposition Log(m Cl ) kg ha -1 yr -1 From the National Atmospheric Deposition Program (NADP)

33. Aerosol Chloride is Ubiquitous  ClNO2 >90%  ClNO2 >50% Q. Zhang, et al GRL 2007

34. NO x, Air Quality, and Climate Forcings Catalyze ozone production Regulate oxidant abundance Shindell, et al Science 2009 NO x NO x emissions couple air quality and climate concerns

35. Chlorine Activation by N 2 O 5 : Model Predictions 1996 Erickson, et al JGR Global ClNO 2 Production From Sea Spray  0.06 Tg Cl/yr 2007 Pechtl and von Glasow, GRL Chlorine Activation in Long Island Sound Maximum ClNO 2 mixing ratio ~ 50 pptv (only on “first night”) 1-2 days downwind negligible Always less than 5% of Cl atom source

36. Atomic Chlorine: powerful oxidant CH 4 + OH  Products CH 4 + Cl  Products  CH4 oxidant 0.05 ppt ~10 years 0.05 ppt 0.5 years

37. Tropospheric Cl atoms We know they exist, but their sources, distribution, and abundance are poorly constrained Baring Head, New Zealand Jobson, et al JGR 1994 Platt, et al ACP 2004

38. Where there’s chloride for ClNO 2 production U.S. IMPROVE Network fine-mode particle chloride ClNO 2 Yield From U.S. NADP precipitation Cl - and NO 3 - Chlorine Availability: [Cl - ] / f[NO 3 - ]

39. Current Constraints from ClNO 2 Observations 1. TexAQS – GoMACCS [ClNO 2 ] ~ 50 - > 1000 ppt Osthoff, et al, Nature Geo. 2008 1 2. ICEALOT-LILAQS [ClNO 2 ] ~ 50 - > 1000 ppt Kercher, et al, AMT 2009 2 3. ACCRONIM-Boulder, CO [ClNO 2 ] ~ 50 – 450 Thornton, et al submitted 2009 3

40. Current Constraints from ClNO 2 Observations 1. TexAQS – GoMACCS [ClNO 2 ] ~ 50 - > 1000 ppt Osthoff, et al, Nature Geo. 2008 1 2. ICEALOT-LILAQS [ClNO 2 ] ~ 50 - > 1000 ppt Kercher, et al, AMT 2009 2 3. ACCRONIM-Boulder, CO [ClNO 2 ] ~ 50 – 450 pptv Thornton, et al submitted 2009 3

41. Where there’s NO x Courtesy of NASA GSFC

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

44. Tropospheric Chlorine Cycling Cl Cl-Xactivation CxHyCxHyCxHyCxHy acid displacement Cl - HCl sea spray ~10,000 Tg Anthro. + 3 – 5 Tg Graedel and Keene, GBC,1995 22-35 Tg* *From methane isotopes measured in remote SH MBL Platt, ACP 2004 Allan, JGR 2007

45. Chemical Modeling Example - 1  ClNO2 ~0.14 Feb 15 – 16 th -highest ClNO 2 -low winds -constant yield captures ClNO 2 growth