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

12.04.2007

3^rd GEOS-Chem USERS` MEETING, Harvard University

Lok Lamsal and Randall Martin

Department of Physics and Atmospheric

Science, Dalhousie University

James Gleason

Goddard Space Flight Center

NASA

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Motivation

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• 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 PM_2.5
• Limited number of sites
• Global map of surface NO₂ not possible without satellite measurements

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Surface measurement sites in US and Canada

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OMI tropospheric NO₂ columns as a proxy for deriving surface NO₂

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• Tropospheric column correlated with NO₂ at surface (Ordóñez et al., 2006)
• Tropospheric column a proxy
• Similar work for ground level PM_2.5 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

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

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Houston: 29°N-31°N, 96.25°W-93.75°W

Texas Air Quality Study aircraft campaign

16 August-13 September 2000

Averaged over OMI overpass time

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NO₂ mixing ratio inferred from OMI

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Comparison between OMI surface NO₂ and in situ measurements

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• 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

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

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Comparison based on land use

ratio

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Why is OMI surface NO₂ lower than in situ measurements?

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Ground based instruments (equipped with molybdenum converter) overestimate surface NO₂.

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• 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

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• Determine correction factor from GEOS-CHEM

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• Correction factor 🢣

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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