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Surface nitrogen dioxide concentrations Surface nitrogen dioxide concentrations

inferred from Ozone Monitoring Instrument inferred from Ozone Monitoring Instrument

(OMI)(OMI)

12.04.2007 3rd 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

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

OMI grids

GEOS-CHEM grid

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2

2 2NO

NNO N

O GEOS-CHEMO

OMI OMIS T X S

T

Need model profile & OMI tropospheric column NO2.

GEOS-CHEM NO2 profile

shape consistent with in situ measurements (Martin et al.,2004)

GEOS-CHEM

In situ

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

About 300 US & Canadian stations

Collocation radius 12 km, overpass time

Agreement incredible at Essex

r = .75

r = .48

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Comparison of ground based and OMI surface NO2

r = .65

r = .27

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Correlation of OMI NO2 with surface measurements

Correlation coefficient for 307 stations

Correlation coefficient higher for polluted regions

Year 2005

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Comparison based on land use

rati

o

Ground based

GEOS-CHEM

rati

oGround based

OMI

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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

interference large in summer

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Correction of GB measurements for interference from HNO3, PAN, and alkyl

nitrates

Determine correction factor from GEOS-CHEM

Correction factor 2

2 3

NO

NO +HNO +PAN+alkyl nitrates

Seasonal means of correction factor

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Correction of GB measurements for interference

Correction factor

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Correction of GB measurements for interference

Seasonal means of surface NO2 (2005)

GB after

correction

OMI

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