Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime
Alyson Baergen and D.J. DonaldsonApril 15, 2014
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Grime
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Grime
- Aesthetics of window soiling- Influence cycling of contaminants–Compartment for partitioning–Facilitate pollutant run off
- Reactive substrate – HNO3
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
HNO3 as a NOx Sink
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NO NO2
O2O3
RO2 RO
OH
HNO3
N2O5
O3NO3
NO2
OH
HONO
OHNH4NO3
NH3
Surface sources of HNO3
2NO2 + H2O HNO3+HONO
N2O5 + H2O 2 HNO3
Photochemical Processing
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Surfaces as Photochemical Sources
HNO3
NONO2
HONON2O
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
Why grime?
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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
Grime Composition
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DecemberOctober
• (1.5±0.2)ng/cm2 of NO3- for samples collected over 4 weeks
• Between 6 and 45% of the extractable ions by mass.
Method: Grime collected directly on ATR-FTIR crystal for 1 week and illuminated with solar simulator
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Nitrate Photolysis on Real Grime
Baergen, A. M.; Donaldson, D. J. Environ Sci Technol 2013
NO3-
ν3 asymmetric stretch
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Nitrate Photolysis on Real Grime
1Zhou, X. et al. J. Geophys Res Lett 2003 Baergen, A. M.; Donaldson, D. J. Environ Sci Technol 2013
J=3x10-2 min-1
Water Glass1 GrimeLifetime
(Adjusted to Summer Sun)
116 days ~13 hours 14 min
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Nitrate Photolysis on Real Grime
GrimeGrime w/ HNO3
Hydrocarbon Grease
Method: Add gas phase HNO3 to grime or film composed of hydrocarbon or grease. Illuminate with
solar simulator and monitor with ATR-FTIR
NO+
(NO, NO2, 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. HNO3
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Gas Phase Products from Grime Photochemistry: EI-MS
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Method: Incoherent Broad Band Cavity Enhanced Spectroscopy to detect gas phase products from illuminated
grime collected for 1 week with additional HNO3
Gas Phase Products from Grime Photochemistry: IBBCEAS
• Production is enhanced when the sample is exposed to high RH
HONO: ~ 3x1011 molec cm-3
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H2O Presence on Real GrimeMethod: Grime collected directly on crystal for Quartz Crystal
Microbalance for 1 week and exposed to increasing then decreasing RH
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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 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-NO2 hν R’ + HONOR-ONO hν R’C=O + NO
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Method: Apiezon N vacuum grease exposed to head space of conc. HNO3 and analyzed by ATR-FTIR
Condensed Phase Products from HNO3 and Hydrocarbon Grease
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Method: HNO3-exposed grease was illuminated and analyzed by ATR-FTIR
Condensed Phase Products from HNO3 -Exposed Grease Photochemistry
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Method: Detected products from grease treated with HNO3 with photochemical Knudsen cell putting long pass
filters in the beam of the light source
NO+
Gas Phase Products from HNO3 - Exposed Grease Photochemistry: EI-MS
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Method: IBBCEAS to detect gas phase products from illuminated HNO3-exposed grease
Gas Phase Products from HNO3 - Exposed Grease Photochemistry: IBBCEAS
HONO:~ 2x1012 molec cm-3
NO2: ~1x1012 molec cm-3
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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
Reaction Pathways
R-NO2 hν R’ + HONOR HNO3 R-NO2, RONOx
R-ONO hν R’C=O + NOR-ONOx/R-NO2 hν R’ + NO2
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