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Ground-level nitrogen dioxide concentrations Ground-level nitrogen dioxide concentrations

inferred from the satellite-borne Ozone inferred from the satellite-borne Ozone

Monitoring InstrumentMonitoring Instrument

Lok Lamsal and Randall Martin with contributions from Martin Steinbacher, Empa Edward Celarier, SGT Inc. Eric Bucsela, NASA GSFC Edward Dunlea, CIRES Joseph Pinto, U.S. EPA

13.08.2007

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Nitrogen dioxide

Is a reddish-brown gas and has a sharp biting odor

Is a prominant toxic air pollutant

Current WHO guideline: 200 µg/m3 (hourly average), 40 µg/m3 (annual average)

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NOx sources

aircraft1.05%

stratosphere0.21%

fossil fuel55.25%

biomass burning13.65%

lightning12.60%

soil12.60%

biofuel4.62%

Surface sources: 85%

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NOx: Impacts on public health and the environment

Acid deposition

Toxic products

Visibility impairment Eutrophication

Health effects

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Ambient NO2 as indicator of toxic air pollution

Strong association between between NO2 and mortality.

NO2 strongly

correlated with other air pollutants

NO2 can serve as an

indicator of level of toxicity in air

VOC

PAH

Brook et al., 2007

Correlation of NO2 and PM2.5 with certain

PAH and VOC

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Ground-based NO2 measurements

NO2 measuring instruments:CLNOx

(molybdenum, photolytic), DOAS, LIF, TILDAS

Sparse fixed sites

Surface NO2 shows a large gradient

Don‘t reflect personal exposure to NO2

Satellite-derived NO2 would be very

useful

Not possible to retrieve surface NO2

from satellite

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Tropospheric column as a proxy for surface NO2

Tropospheric column retrieval from satellite

Strong relation between tropospheric columns and surface NOx

emissions

NO2 in the lower mixed

layer makes 70-90% contribution to tropospheric column

Aim: derive ground-level NO2 from OMI

San Francisco

Los Angeles Phoenix

Houston

Dallas

Chicago

Toronto

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NO2 from OMI

Launch 15th July 2004 onboard EOS-Aura

OMI instrument is from the contribution from NIVR and FMI

Spectral coverage: 270-500 nm

Ozone, NO2, SO2, HCHO, BrO, OClO,

cloud and aerosol properties Horizontal resolution ≥ 13 x 24 km2

Daily global coverage

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GEOS-Chem

GEOS-CHEM

In situ

Need of information on NO2

profile from a 3D model GEOS-Chem at 2x2.5,

version 7-03-06, 12:00-14:00 local time

GEOS-Chem NO2 profile

shape consistent with in situ measurements

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Approach to derive surface NO2

2

2

2 2NO

NNO N

O GEOS-CHEMO

OMI OMIS T X S

T

GEOS-CHEMIn situ

GEOS-Chem NO2 [ppbv]

2 2

tropopause

NO

surface

T NO dh

2

2

2 2NO

NNO N

O GEOS-CHEMO

OMI OMIS T X S

T

SATSAT

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Sensitivity studies: Effect of model profileOMI grids

GEOS-Chem grids

Error < 10%

in polluted

areaspolluted

unpolluted

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In situ NO2 measurements: Chemiluminescent NOx analyzer

Chemiluminescent NOx analyzer does not provide true NO2

NO + O3 → NO2* + O2

NO2* → NO2 + h

NO mode

NOx mode

NO2 → NO

NO2 = NOx - NO

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Comparison with DOAS measurements

OMI over pass time (12.00 to 14:00 local time)

Interference~50%

HNO3~60%

∑AN~10-30%

Mexico City

Apr 2003

Dunlea et al. 2007

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Comparison with photolytic analyzers

Taenikon/Switzerland

Jan-Dec 2000

Steinbacher et al. 2007

Interference:20-60%

PAN:30-50%

HNO3, particulate

nitrates

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Interference in chemiluminescent analyzers with molybdenum converter

Compounds Conversion

efficiency

Experiments

NO, NO2, ethyl nitrate ~ 100% Winer et al.,

1974

PAN 92% Winer et al.,

1974

HNO3, PAN, n-propyl

nitrate, n-butyl nitrate

≥98% Grosjean and

Harrison, 1985

Ammonia, gas phase

olefins, particulate

nitrate

No significant

interference

Dunlea et al.,

2007

Difficult issue: Loss of HNO3 on stainless steel of inlet

Difficult to quantify the conversion efficiency

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Correction of interference

Bias = 40%

Bias = 8%

Taenikon, Switzerland

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2 3

NOCF=

NO + AN+0.95×PAN+0.35×HNO

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Correction for interference for USA and Canada

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Comparison between OMI and in situ measurements

Selected 214 stations201 US and 13 Canada

Collocation criteriaRadius 10 km, time = 12:00 to

14:00 local time

► Mean correlation 0.51, maximum 0.86

► Stronger correlation in polluted areas

Correlation map

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Comparison between OMI and in situ measurements

►Uncorrected >

corrected by

up to a factor of 3

►OMI and corrected

in situ measurements

consistent

►summer minima

►OMI<corrected in

situ measurements

DJF MAM JJA SON

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Comparison between OMI and in situ measurements

J F M A M J J A S O N D

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Comparison between OMI and in situ measurements according to land type

Urban, suburban, rural

Mean bias -21 to -48%

Underestimation of tropospheric column by OMI

Seasonal bias in OMI retrievalsOMI-Chemiluminescent

bias=chemiluminescient

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Seasonal bias in OMI retrievals

33% -20% -58% -15%

DJF MAM JJA SON

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Conclusions

We derived ground-level NO2 from OMI using information from

the GEOS-Chem model.

OMI-derived surface NO2 is robust to model profile in polluted

areas. In situ measurements have significant interference from PAN,

alkyl nitrates, and HNO3

Following laboratory studies and field measurements, we developed a correction algorithm to the in situ measurements.

We compared OMI-derived surface NO2 with the corrected in

situ measurements from US and Canadian stations to validate our approach

OMI derived surface NO2 agrees to 21 to 48% with the corrected

in situ measurements. The remaining discrepancy is associated with the OMI retrievals. Submitted to JGR atmospheres