Validation of OMI and SCIAMACHY tropospheric NO2 columns using

DANDELIONS ground-based data

J. Hains1, H. Volten2, F. Boersma1, F. Wittrock3, A. Richter3, T.Wagner4, M. Van Roozendael5, R. Dirksen1,

M. Kroon1, and P. Levelt1

1. KNMI, De Bilt, The Netherlands, contact:hains@knmi2. RIVM, Bilthoven, The Netherlands

3. University of Bremen, Bremen, Germany4. Max-Planck Institute for Chemistry

5. BIRA-IASB, Brussels, Belgium

OMI Science Team Meeting June 25, 2008

Outline

• Describe tropospheric NO2 observations.• Comparisons among ground based

instruments.• Compare ground based instruments with

satellite.• Investigate influence of measurements on OMI

tropospheric NO2 retrieval. • Introduce possible NO2 instrument comparison

– Summer 2009

Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY

DANDELIONS 2006

• Time 8-13 and 20-22 September 2006.

• Conditions Clear skies and fair weather, Cabauw The Netherlands.

• Ground based instruments 3 MAXDOAS (BIRA, University of Bremen and University of Heidelberg), RIVM lidar profiles and in-situ concentrations from chemiluminescence instruments at surface and on top of 200 m tower.

– RIVM aerosol lidar observed the planetary boundary layer height (PBL).

– Ground based instruments sample different directions.

• Satellites OMI and SCIAMACHY DOMINO products.

Cabauw

industry

industry

Clean air

CESAR

The Site

industry

PBL

In-situ MAX

DOASLidar

Scattering

Conc. (7 altitudes) + PBL height (aerosol lidar) VCpbl

OMI and SCIAMACHY DOMINOTropospheric NO2 vertical column (VCt)

SCIAMACHY pixel size 30x60 km2.OMI pixel size 13x24 km2 (nadir). VCt = VCpbl + VCft

Concentration (0, 200 m) + PBL height (aerosol lidar) VCpbl

Slant column + geo AMF VCt

Comparisons among ground

based instruments

1:1

1:1

Comparisons among ground

based instruments

1:1

1:1 In-situ observes more NO2 than lidar NOy bias (PAN, HNO3 etc.)

1:1Comparisons among ground

based instruments

1:1 Comparisons are good (instruments sample different directions).

MAXDOAS observes more NO2 than lidar in lidar integration free tropospheric NO2 = 0.

Comparisons with satellite

Comparisons are good considering differences in spatial and temporal resolution.

+ pixel size <650 km2

+ pixel size > 650 km2

+ SCIAMACHY

1:1

1:1

1:1

1:1Comparisons with satellite

+ pixel size <650 km2

+ pixel size > 650 km2

+ SCIAMACHY

1:1

3 MAXDOAS, lidar and in-situ

+ pixel size <650 km2

+ pixel size > 650 km2

+ SCIAMACHY

OMI and SCIAMACHY DOMINO products are within 33% of ground based observations.

Plausible explanations for the difference

• MAXDOAS and satellite use different AMF.

• In-situ has positive bias due to NOy interference.

• OMI and SCIAMACHY are affected by clouds.

• Satellite observations represent a large ground pixel (e.g. OMI nadir pixel is 13 x 24 km2) while ground-based observations are point measurements.

• Ground based instruments have not been thoroughly compared with each other or compared with in-situ aircraft profiles - plan for future campaign.

Level 1B Slant column NO2

Stratospheric Slant column

NO2

Tropospheric Slant column

NO2

Stratospheric Vertical

column NO2

Tropospheric Vertical

column NO2

TM4-DOMINO

AMF Strat AMF Trop

• TM4- global chemistry transport model run with assimilated OMI products

• TM4 produces NO2 profiles

• These NO2 profiles are used to calculate AMFs (air mass factors).

OMI tropospheric NO2 algorithmTM4-

DOMINO

TM4-DOMINO

Can we improve the algorithm ?

• Examine a-priori profile shape in TM4 model.

• Compare TM4 profile with lidar profile

• How does NO2 change with revised AMF.

Steps to Compare lidar with TM4 NO2

1. Interpolate/Extrapolate Lidar.

2. Regrid observation to 1hpa grid.

3. Integrate NO2 between TM4 levels partial columns.

OMI (original and revised AMF) and average ground based NO2 observations.

Small changes.

TM4 profiles are good assumptions.

0.E+00

1.E+16

2.E+16

3.E+16

0.E+00 1.E+16 2.E+16 3.E+16Average ground based NO2 (molecules cm-2)

OM

I NO

2 (m

ole

cu

les

cm

-2)

original

1:1

r = .76

Statistics for comparisons 

Percent difference

standard deviation

Correlation coefficient

Original 36% 29% 0.76

Revised 35% 30% 0.77

0.E+00

1.E+16

2.E+16

3.E+16

0.E+00 1.E+16 2.E+16 3.E+16

Average ground based NO2 (molecules cm-2)

OM

I NO

2 (m

ole

cu

les

cm

-2)

original

revised

1:1

r = .77

OMI pixel width < 50 km

0.E+00

1.E+16

2.E+16

3.E+16

20060908 20060909 20060910 20060911 20060912 20060921

Date

NO

2 (

mo

lecu

les

cm-2

)

OMI (original AMF)

OMI (revised AMF)

average ground based

Compare TM4 and lidar profiles

TM4 NO2 peaks at lower level than lidar.

OMI less sensitive to original TM4 profile.

AMF is too small.

OMI NO2 is too large.

Conclusions

• Ground based NO2 instruments compare well with each other (r ~ .6).

• OMI and SCIAMACHY (DOMINO) compare well with average ground based NO2 (within 33%).

• Comparisons among instruments are good considering the differences in retrieval techniques and temporal and spatial resolution.

• These results are fair weather biased.

• Including lidar tropospheric NO2 profiles in the AMF calculation did not affect the AMF TM4 profiles are good assumptions.

Tentative plans for CEOS/GEOMON NO2 instrument comparison

Possible Goals:

• Surface campaign (like DANDELIONS)

• ~15 instruments (MAXDOAS, lidar and in-situ monitors).

– NDACC blind test.

• Observations support OMI and SCIAMACHY validation.

• 1st part - compare instruments.

• 2nd part - move the instruments to sites wihtin a pixel.

Improve understanding of NO2 variability in the area of a satellite pixel.

Location: Europe, possibly Cabauw, The Netherlands

When: Summer 2009

Participants: Europe, N. America, Asia

+ pixel size <650 km2

+ pixel size > 650 km2

+ SCIAMACHY

Operational

DOMINO

Comparisons with DOMINOPercent

differenceStandard deviation Slope

Correlation coefficient (r)

Number of pixels

Validation days 33% 32% 0.8 0.8 19

Validation days with small pixels 24% 26% 1.3 0.9 7

Comparisons with Standard productPercent

differenceStandard deviation Slope

Correlation coefficient (r)

Number of pixels

Validation days 33% 27% 0.7 0.8 19Validation days with small pixels 28% 21% 0.9 0.8 6

Compare TM4 with lidar

profile

Compare TM4 with lidar profile

Lidar profile measurements

1sin ( ) 1off zen

trop

SCD SCDVC

LOS

MAXDOAS Tropospheric NO2 VCD retrieved using geometric AMF

NO2 layer LOS

SCDoff

SCDzen