Surface nitrogen dioxide concentrations inferred from Ozone Monitoring Instrument (OMI)

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• Surface nitrogen dioxide concentrations inferred
  from Ozone Monitoring Instrument (OMI)
  

Lok Lamsal and Randall Martin Department of
Physics and Atmospheric Science, Dalhousie
University
James Gleason Goddard Space Flight Center NASA
12.04.2007
3rd GEOS-Chem USERS MEETING, Harvard University
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Motivation

• Surface NO2 is a toxic pollutant that affects
  human health
• Association between surface NO2 and
  non-accidental mortality (Burnett et al., 2004
  Brook et al., 2007)
• Association stronger than for PM2.5
• Limited number of sites
• Global map of surface NO2 not possible without
  satellite measurements

Surface measurement sites in US and Canada
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OMI tropospheric NO2 columns as a proxy for
deriving surface NO2

• Tropospheric column correlated with NO2 at
  surface (Ordóñez et al., 2006)
• Tropospheric column a proxy
• Similar work for ground level PM2.5 from van
  Donkelaar et al., 2006 Liu et al., 2004

Global distribution of tropospheric column NO2
(Sep. 2005)
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Derivation of surface NO2 from OMI

• Need model profile OMI tropospheric column NO2.
• GEOS-CHEM NO2 profile shape consistent with in
  situ measurements (Martin et al.,2004)

Averaged over OMI overpass time
Houston 29N-31N, 96.25W-93.75W Texas Air
Quality Study aircraft campaign 16 August-13
September 2000
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NO2 mixing ratio inferred from OMI
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Comparison between OMI surface NO2 and in situ
measurements

• About 300 US Canadian stations
• Collocation radius 12 km, overpass time
• Agreement incredible at Essex

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Comparison of ground based and OMI surface NO2
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Correlation of OMI NO2 with surface measurements

• Correlation coefficient for 307 stations
• Correlation coefficient higher for polluted
  regions

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Comparison based on land use
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Why is OMI surface NO2 lower than in situ
measurements?
Ground based instruments (equipped with
molybdenum converter) overestimate surface NO2.

• Equipped with molybdenum converter
• Interference from HNO3, PAN, alkyl nitrates
• Instrument with photolytic converter more
  accurate

Schaub et al., 2006 Ordóñez et al., 2006 Dunlea
et al., 2007
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Correction of GB measurements for interference
from HNO3, PAN, and alkyl nitrates
Seasonal means of correction factor
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Correction of GB measurements for interference
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Correction of GB measurements for interference
Seasonal means of surface NO2 (2005)
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