Air Pollution/Environmental Technology laboratory Initial results on OMI NO 2 Validation during CINDI A contribution to the BIRA Cindi Workshop Yipin Zhou,

Air Pollution/Environmental Technology laboratory

Initial results on OMI NOInitial results on OMI NO22 Validation Validation

during CINDIduring CINDI

A A contributioncontribution to the BIRA Cindi Workshop to the BIRA Cindi Workshop

Yipin ZhouYipin Zhou, Dominik Brunner, and Brigitte Buchmann, Dominik Brunner, and Brigitte Buchmann

Empa, Swiss Federal Laboratories for Materials Testing and Research Empa, Swiss Federal Laboratories for Materials Testing and Research Dübendorf, SwitzerlandDübendorf, Switzerland

With special thanks toWith special thanks to

Florence GoutailFlorence Goutail Folkert BoersmaKatrijn Clemer

BIRA

M. Ernst

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Outlook

1.1. Comparison of SAOZ NOComparison of SAOZ NO22 column with In-situ column with In-situ column calculated with Lidar and Ceilometer column calculated with Lidar and Ceilometer boundary height.boundary height.

2.2. Introduction to Empa OMI NOIntroduction to Empa OMI NO22 retrieval. retrieval.

3.3. Comparison of OMI NOComparison of OMI NO22 column with SAOZ. column with SAOZ.


In-situ vs SAOZ NO2 columns (10 mins resolution)

LIDAR LIDAR PBL topsPBL tops

11 < UTC < 1811 < UTC < 18

June 24thJune 24th


Ceilometer Ceilometer PBL topsPBL tops

11 < UTC < 1811 < UTC < 18

In-situ vs SAOZ NO2 columns (10 mins resolution)


In-situ vs SAOZ NO2 columns (1 hour averages)11 < UTC < 1811 < UTC < 18


OMI tropospheric NO2 retrieval

1.1. Based on DOMINO retrieval (TM4 a-priori, SCD, cloud Based on DOMINO retrieval (TM4 a-priori, SCD, cloud algorithm)algorithm)

2.2. Improved AMF calculation (high spatial resolution Improved AMF calculation (high spatial resolution terrain height, considering BRDF effect based on high terrain height, considering BRDF effect based on high spatial and temporal resolution MODIS data set)spatial and temporal resolution MODIS data set)

3.3. On-line calculation with LIDORT 3.3On-line calculation with LIDORT 3.3


SZA

Surface reflectance generally depends on solar zenith angle (SZA) Surface reflectance generally depends on solar zenith angle (SZA) and viewing zenith angle (VZA)and viewing zenith angle (VZA)


),,,()(),,,()()(),,,( geogeovolvoliso KfKffBRF

ffvol vol in Julyin July ffvolvol in November in November

volumetricvolumetric geometricgeometric


VZA

BR

F

BRF

Example in summer (July)Example in summer (July)

Typical OMI swathTypical OMI swath


Relative error in NORelative error in NO22



Mean NOMean NO22 VTCs averaged over the years 2006 and 2007 VTCs averaged over the years 2006 and 2007 (July, Nov)(July, Nov)


OMI pixel selection

For each orbit (VZA <65), find the pixel closest to the Cabauw tower.For each orbit (VZA <65), find the pixel closest to the Cabauw tower.Average if there are two pixels with similiar distance.Average if there are two pixels with similiar distance.


Row anomaly (28Row anomaly (28thth-40-40thth,46,46thth-50-50thth,53,53thth-54-54thth pixels are affected ) pixels are affected )

Empa retrieval (screening, cloud fraction < 25%) Empa retrieval (screening, cloud fraction < 25%)

OMI vs SAOZ


OMI vs SAOZn=12 (only good pixels)n=12 (only good pixels)

n=20 (including row anomaly pixels)n=20 (including row anomaly pixels)

Cloud radiance fractionCloud radiance fraction

(cloud fraction < 25%)(cloud fraction < 25%)


OMI vs SAOZ

Cloud screening is necessary for validationCloud screening is necessary for validation


Conclusions

1.1. NONO22 columns constructed from the in-situ measurement columns constructed from the in-situ measurement

agrees well with the SAOZ columns. Better agreement agrees well with the SAOZ columns. Better agreement is found from the in-situ columns calculated with is found from the in-situ columns calculated with boundary height from Lidar and SAOZ retrieved with boundary height from Lidar and SAOZ retrieved with IASB AMFs calculated using their NOIASB AMFs calculated using their NO22 and aerosol and aerosol profiles .profiles .

2.2. For the pixels with cloud fraction smaller than 25%, the For the pixels with cloud fraction smaller than 25%, the correlation of the OMI NOcorrelation of the OMI NO22 columns and the SAOZ columns and the SAOZ

columns are better than 0.6. Empa retrieval shows good columns are better than 0.6. Empa retrieval shows good agreement even when the sample size is quite small. agreement even when the sample size is quite small. Albedo effect is not obvious during this time period.Albedo effect is not obvious during this time period.

3.3. Cloud shows larger impact on the NOCloud shows larger impact on the NO22 retrieval than the retrieval than the

row anomaly. row anomaly.

Documents

Air Pollution/Environmental Technology laboratory Initial results on OMI NO 2 Validation during CINDI A contribution to the BIRA Cindi Workshop Yipin Zhou,