1. Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime Alyson Baergen and D.J. Donaldson April 15, 2014

2. 2 Grime

3. 3 -Aesthetics of window soiling -Influence cycling of contaminants – Compartment for partitioning – Facilitate pollutant run off -Reactive substrate – HNO 3 Lombardo, T. et al. Atmos Environ 2005; Diamond, Wu R.W. et al Atmos Environ 2008; M.L. et al. Chemosphere 2001; Baergen A. et al Environ Sci Technol 2013

4. HNO 3 as a NO x Sink 4 NO NO 2 O2O2 O3O3 RO 2 RO OH HNO 3 N2O5N2O5 O3O3 NO 3 NO 2 OH HONO OH NH 4 NO 3 NH 3 Surface sources of HNO 3 2NO 2 + H 2 O HNO 3 +HONO N 2 O 5 + H 2 O 2 HNO 3

5. Photochemical Processing 5 Surfaces as Photochemical Sources HNO 3 NO NO 2 HONO N 2 O Jacobi, H.-W.;et al Environ Sci Technol 2013; Rubasinghege, G.; Grassian, V. H. J Phys Chem A 2009; Zhou, X.; et al. Nature Geosci 2011

6. Why grime? 6 Grime is ubiquitous on impervious surfaces Less than 1 micron in thickness resulting in large surface area to volume Nitrate is present within grime Lam, B. et al Atmos Environ 2005; Alfaro, S. C. et al. Atmos Environ 2012

7. Grime Composition 7 December October (1.5±0.2)ng/cm 2 of NO 3 - for samples collected over 4 weeks Between 6 and 45% of the extractable ions by mass.

8. Method: Grime collected directly on ATR-FTIR crystal for 1 week and illuminated with solar simulator 8 Nitrate Photolysis on Real Grime Baergen, A. M.; Donaldson, D. J. Environ Sci Technol 2013 NO 3 - ν 3 asymmetric stretch

9. 9 Nitrate Photolysis on Real Grime 1 Zhou, X. et al. J. Geophys Res Lett 2003 Baergen, A. M.; Donaldson, D. J. Environ Sci Technol 2013 J=3x10 -2 min -1 WaterGlass 1 Grime Lifetime (Adjusted to Summer Sun) 116 days~13 hours14 min

10. 10 Nitrate Photolysis on Real Grime Grime Grime w/ HNO 3 Hydrocarbon Grease Method: Add gas phase HNO 3 to grime or film composed of hydrocarbon or grease. Illuminate with solar simulator and monitor with ATR-FTIR

11. NO + (NO, NO 2, HONO) Method: Photochemical Knudsen cell with Electron-Impact Quadropole Mass Spectrometer. Grime collected on pyrex sample holders for 1 week then exposed to headspace above conc. HNO 3 11 Gas Phase Products from Grime Photochemistry: EI-MS

12. 12 Method: Incoherent Broad Band Cavity Enhanced Spectroscopy to detect gas phase products from illuminated grime collected for 1 week with additional HNO 3 Gas Phase Products from Grime Photochemistry: IBBCEAS Production is enhanced when the sample is exposed to high RH HONO: ~ 3x10 11 molec cm -3

13. 13 H 2 O Presence on Real Grime Method: Grime collected directly on crystal for Quartz Crystal Microbalance for 1 week and exposed to increasing then decreasing RH

14. 14 Lam, B. et al Atmos Environ 2005; Alfaro, S. C. et al. Atmos Environ 2012; Aubin, D G. et al J.Phys Chem A. 2007; Miet et al Atmo Environ 2009; Monge, M E. et al PNAS 2010; Stemmler, K. et al Atmos Chem Phys 2007; Sosedova, T. et al Atmos Chem Phys 2007 Zhou, X.; et al. Nature Geosci 2011 ; Han et al Atmos Environ 2013 Organic Chemistry and NO x /HONO Organics could play a role in reducing NO 2 to HONO Photoenhanced on soot, humic acid, polyphenolic compounds HONO/NO x ratios of 1-5 for HNO 3 photolysis on surface containing organic compounds and moisture Organics could react with HNO 3 or NO 2 to form R-ONO x and R-NO 2 species which can photolyze Observed on PAH film and soot R-NO 2 hν R’ + HONO R-ONO hν R’C=O + NO

15. 15 Method: Apiezon N vacuum grease exposed to head space of conc. HNO 3 and analyzed by ATR-FTIR Condensed Phase Products from HNO 3 and Hydrocarbon Grease

16. 16 Method: HNO 3 -exposed grease was illuminated and analyzed by ATR-FTIR Condensed Phase Products from HNO 3 - Exposed Grease Photochemistry

17. 17 Method: Detected products from grease treated with HNO 3 with photochemical Knudsen cell putting long pass filters in the beam of the light source NO + Gas Phase Products from HNO 3 - Exposed Grease Photochemistry: EI-MS

18. 18 Method: IBBCEAS to detect gas phase products from illuminated HNO 3 -exposed grease Gas Phase Products from HNO 3 - Exposed Grease Photochemistry: IBBCEAS HONO:~ 2x10 12 molec cm -3 NO 2 : ~1x10 12 molec cm -3

19. 19 Grime mediates fast NO 3 - photolysis Water is present on the film and is important for the chemistry HONO is a major product of the photochemistry Grime’s organic fraction of may play a role Reaction Pathways R-NO 2 hν R’ + HONO R HNO 3 R-NO 2, RONO x R-ONO hν R’C=O + NO R-ONO x /R-NO 2 hν R’ + NO 2

20. Urban grime may mediate a photochemical pathway for the cycling of nitrogen oxides back into the atmosphere Baergen, A. M.; Donaldson, D. J. Photochemical Renoxification of Nitric Acid on Real Urban Grime Environ Sci Technol 2013 Baergen, A. M.; Donaldson, D. J. Formation of Reactive Nitrogen Oxides from the Photochemistry of Urban Grime. In prep abaergen@chem.utoronto.ca