Embed Size (px)
DESCRIPTION
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. - PowerPoint PPT Presentation
Citation preview
Heterogeneous Photochemistry of Nitrogen Oxides on Urban Grime
Alyson Baergen and D.J. DonaldsonApril 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. 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
4
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
5
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?
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
Grime Composition
7
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
8
Nitrate Photolysis on Real Grime
Baergen, A. M.; Donaldson, D. J. Environ Sci Technol 2013
NO3-
ν3 asymmetric stretch
9
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
10
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
11
Gas Phase Products from Grime Photochemistry: EI-MS
12
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
13
H2O Presence on Real GrimeMethod: Grime collected directly on crystal for Quartz Crystal
Microbalance for 1 week and exposed to increasing then decreasing RH
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 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
15
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
16
Method: HNO3-exposed grease was illuminated and analyzed by ATR-FTIR
Condensed Phase Products from HNO3 -Exposed Grease Photochemistry
17
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
18
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
19
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
![The Environmental Photochemistry of Oxide Surfaces and the … · 2017-04-10 · [24] or mineral oxides [25, 26] under atmospheric condi-tions. Indeed, the high water vapor pressure](https://img.pdfslide.us/doc/110x75/5f71cb8bcb4a211a394de083/the-environmental-photochemistry-of-oxide-surfaces-and-the-2017-04-10-24-or.jpg)
