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Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime

Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime. Alyson Baergen and D.J. Donaldson April 15, 2014. Grime. Grime. Aesthetics of window soiling Influence cycling of contaminants Compartment for partitioning Facilitate pollutant run off Reactive substrate – HNO 3.

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Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime

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

  2. Grime

  3. Grime • Aesthetics of window soiling • Influence cycling of contaminants • Compartment for partitioning • Facilitate pollutant run off • Reactive substrate – HNO3 Lombardo, T.et al. AtmosEnviron 2005; Diamond, Wu R.W. et al Atmos Environ 2008; M.L. et al. Chemosphere 2001; Baergen A. et al Environ SciTechnol2013

  4. HNO3 as a NOx Sink Surface sources of HNO3 RO2 OH RO NO NO2 2 HNO3 N2O5 + H2O NO2 O3 HONO NO3 N2O5 2NO2+H2O HNO3+HONO OH NH3 OH HNO3 NH4NO3 O2 O3

  5. Photochemical Processing Surfaces as Photochemical Sources NO NO2 HONO N2O HNO3 Jacobi, H.-W.;etalEnvironSciTechnol2013;Rubasinghege, G.; Grassian, V. H. J Phys Chem A 2009; Zhou, X.; et al. Nature Geosci2011

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

  7. Grime Composition October December • (1.5±0.2)ng/cm2of NO3- for samples collected over 4 weeks • Between 6 and 45% of the extractable ions by mass.

  8. Nitrate Photolysis on Real Grime Method: Grime collected directly on ATR-FTIR crystal for 1 week and illuminated with solar simulator NO3- ν3 asymmetric stretch Baergen, A. M.; Donaldson, D. J. Environ SciTechnol 2013

  9. Nitrate Photolysis on Real Grime J=3x10-2 min-1 1Zhou, X. et al. J. Geophys Res Lett2003Baergen, A. M.; Donaldson, D. J. Environ SciTechnol2013

  10. Nitrate Photolysis on Real Grime Method: Add gas phase HNO3 to grime or film composed of hydrocarbon or grease. Illuminate with solar simulator and monitor with ATR-FTIR Grime Grime w/ HNO3 Hydrocarbon Grease

  11. Gas Phase Products from Grime Photochemistry: EI-MS Method: Photochemical Knudsen cell with Electron-Impact QuadropoleMass Spectrometer. Grime collected on pyrexsample holders for 1 week then exposed to headspace above conc. HNO3 NO+ (NO, NO2, HONO)

  12. Gas Phase Products from Grime Photochemistry: IBBCEAS Method: Incoherent Broad Band Cavity Enhanced Spectroscopy to detect gas phase products from illuminated grime collected for 1 week with additional HNO3 HONO: ~ 3x1011molec cm-3 • Production is enhanced when the sample is exposed to high RH

  13. H2O 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. Organic Chemistry and NOx/HONO • Organics could play a role in reducing NO2 to HONO • Photoenhanced on soot, humic acid, polyphenolic compounds • HONO/NOx ratios of 1-5 for HNO3 photolysis on surface containing organic compounds and moisture • Organics could react with HNO3 or NO2 to form R-ONOx and R-NO2 species which can photolyze • Observed on PAH film and soot R-NO2hν R’ + HONO R-ONOhν R’C=O + NO Lam, B. et al AtmosEnviron 2005; Alfaro, S. C. et al. Atmos Environ 2012;Aubin, D G. et al J.PhysChem A. 2007; Mietet al Atmo Environ 2009;Monge, M E. et al PNAS 2010;Stemmler, K. et al AtmosChemPhys2007;Sosedova, T. et al AtmosChemPhys2007 Zhou, X.; et al . Nature Geosci2011; Han et al Atmos Environ 2013

  15. Condensed Phase Products from HNO3 and Hydrocarbon Grease Method: Apiezon N vacuum grease exposed to head space of conc. HNO3 and analyzed by ATR-FTIR

  16. Condensed Phase Products from HNO3 -Exposed Grease Photochemistry Method: HNO3-exposed grease was illuminated and analyzed by ATR-FTIR

  17. Gas Phase Products from HNO3 - Exposed Grease Photochemistry: EI-MS Method: Detected products from grease treated with HNO3with photochemical Knudsen cell putting long pass filters in the beam of the light source NO+

  18. Gas Phase Products from HNO3 - Exposed Grease Photochemistry: IBBCEAS Method: IBBCEASto detect gas phase products from illuminated HNO3-exposed grease HONO:~ 2x1012 moleccm-3 NO2: ~1x1012 molec cm-3

  19. Reaction Pathways R HNO3 R-NO2, RONOx R-ONOhν R’C=O + NO R-ONOx/R-NO2hν R’ + NO2 R-NO2hν R’ + HONO Grime mediates fast NO3-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

  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 NitricAcid on Real Urban Grime Environ SciTechnol2013 Baergen, A. M.; Donaldson, D. J. Formation of Reactive Nitrogen Oxides from the Photochemistry of Urban Grime. In prep abaergen@chem.utoronto.ca

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