1. Near-Infrared Photochemistry of Atmospheric Nitrites Paul Wennberg, Coleen Roehl, Geoff Blake, and Sergey Nizkorodov California Institute of Technology Ross Salawitch, Geoff Toon Jet Propulsion Laboratory

2. Stratospheric Ozone Photochemistry Courtesy NASA Goddard

3. HO 2 + O 3  OH + O 2 + O 2 OH + O 3  HO 2 + O 2 O 3 + O 3  O 2 + O 2 + O 2 Catalytic destruction of Ozone by HO x Wennberg et al., Science, 266, 398, 1997

4. HO x Photochemistry Sources: O 3 + hν (< 314 nm)  O ( 1 D) + O 2 O ( 1 D) + H 2 O  2 OH Sinks (Direct): OH + HO 2  H 2 O + O 2 Sinks (Indirect): OH + NO 2  HONO 2 OH + HONO 2  H 2 O + O 3 HO 2 + NO 2  HO 2 NO 2 OH + HOONO 2  H 2 O + O 2 + NO 2 OH HO 2 NO, O 3 O3O3

5. Tropospheric O 3 Production OH + CO  CO 2 + HO 2 HO 2 + NO  NO 2 + OH NO 2 + hν (< 450 nm)  NO + O O + O 2  O 3 Net: CO + 2 O 2  O 3 + CO 2 More O 3 production Less O 3 production Jaegle et al., J. Geophys. Res., 105, 3877-3892, 2000. O2O2

7. The Color of Sunlight

9. Peroxy Nitric Acid (HO 2 NO 2 ) Donaldson et al. (1997) proposed that dissociative excitation of OH vibrational overtones in H 2 O 2, HNO 3, and HO 2 NO 2 is an additional source of OH in the atmosphere Wennberg et al. (1999) found unknown photochemical source of OH in the mid-latitude stratosphere with photolysis > 650 nm and suggested HO 2 NO 2 as the carrier D. J. Donaldson et al., Geophys. Res. Lett. 24, 2651 (1997) P. O. Wennberg et al., Geophys. Res. Lett. 26, 1373 (1999) Near IR solar flux is orders of magnitude higher than UV flux

10. Approach HO 2 NO 2 + h  HO 2 + NO 2 OH HO 2 + NO  OH + NO 2 1.IR-photodissociation 2.Conversion into OH 3.Detection of OH Vibrational Dissociation Spectroscopy

11. Experiment Direct overtone pumping of CH / OH stretches in PAN / PNA / HOONO Chemical conversion of photodecomposition products into OH radicals LIF detection of OH in a single photon counting regime

12. Action Spectra Different relative band intensities in FTIR and action spectra Dissociation quantum yields determined by comparing spectra Initial internal energy responsible for dissociation below D 0  (2 1, 240 K)=14%

14. Relative band intensities in action spectra of PNA are T-dependent {  diss (3 1 ) = 1}  Absolute photodissociation cross sections and quantum yields for other bands

16. MkIV HO 2 NO 2 Observations Frequency (cm -1 ) Intensity Residual (%)

17. ? OH + NO 2  ? The Reaction of OH with NO 2 is among the most important reactions in Earth’s atmosphere. By sequestering both HO x and NO x it essentially shuts down reactive photochemistry. It is assumed by all models that the only product formed is nitric acid

18. Part II. HOONO Suspected intermediate of the OH + NO 2 association reaction Proposed intermediate of liquid phase reactions of peroxynitrite ion (ONOO - ) Observed in rare-gas matrices in 1991 Cheng et al. J. Phys. Chem. 95, 2814 (1991) Extensively studied by theory –At least three stable conformers –Bound by 19 kcal/mol Never observed in the gas phase

19. HOONO Atmospheric Significance  Reaction Intermediates  HO + NO 2 HOONO -19 (3 isomers) HONO 2 +7 -48 0 HO 2 + NO HONO 2 HOONO IrreversibleReversible Removal of HO x and NO x No effect

20. HOONO Produce HOONO directly in the gas-phase H 2 + μwave discharge  2 H H + NO 2  OH + NO OH + NO 2 + M  HNO 3 + M OONO OH + NO 2 + M  HOONO + M Photofragment: OONO HOONO + hν  OH + NO 2 Detect OH by LIF Preparation

21. Observed Spectra Stronger peaks assigned to HOONO 2 1 overtones and combination bands Assignment for weaker bands remains ambiguous Intensities affected by photodissociation dynamics D0D0 2 1

22. Observed HOONO Yield HOONO lifetime unknown  lower limit Different conditions  incomparable Higher yield expected for upper troposphere This work (253 K, 20 Torr) Burkholder et al. Dransfield et al. Hippler et al. > 5  3 % (after 300 ms) < 5 %< 10 %Unpublished

23. Future Projects Photochemistry of reaction intermediates –HOCO –HOOOCl –CH 3 OONO Chemistry and kinetics of weakly-bound molecules –CH 3 OONO 2 –CH 3 C(O)OONO 2 –HOONO –HO 2 NO 2 UV photodissociation spectroscopy of atmospheric molecules –CH 3 OOH –HO 2 NO 2

24. Thanks Funding by NASA and NSF Support for Sergey Nizkorodov (just appointed assistant professor of chemistry UC-Irvine) from the Dreyfus foundation. You for your attention!