OMI Nitrogen Dioxide Workshop Ellen Brinksma, Folkert Boersma

OMI NO2 Workshop OMI NRT Validation during INTEX B (F. Boersma) Some statistics on OMNO2 using CAMA

OMI NO 2 Data Products Currently available: Operational NO2 product (“OMNO2”) NASA-KNMI Near-real time product (“NRT”) KNMI, plots daily at Both are based on NO2 operational slant columns, differ in airmass factors, surface albedo, NO2 under clouds. OMNO2NRT Profile shapeClimatologyAssimilation Surface albedo database GOME-derived [Koelemeijer] Koelemeijer/Herman- Celarier Ghost columnNoYes

OMI Validation OMI Team Meeting, 21 May 2006 f < 20%

OMI Validation OMI Team Meeting, 21 May 2006 f < 20%

OMI Validation OMI Team Meeting, 22May 2006 f < 20%

OMI Validation OMI Team Meeting, 22 May 2006 f < 5%

OMI Validation OMI Team Meeting, 22 May 2006 f < 5%

OMI Validation OMI Team Meeting, 22 May 2006 f < 5%

Spiral 1 (down) Spiral 2 (up)

Criteria Cloud fraction < ~20% Use all pixels within box defined by min. and max. lat-lon of the spiral Method 1. Comparison of: - OMI retrieved tropospheric vertical columns vs. - DC8 integrated vertical profiles (i.e. tropospheric columns) (2. Comparison of: - OMI tropospheric slant columns (after subtraction stratosphere) vs. - DC8 predicted trop. slant columns)

4 March: spiral 1 vcd DC8 = molec. cm -2 vcd OMI = 2.62 ± molec. cm -2 (n = 19)

Overview Validation of all clear-sky cases r = 0.89 n = 18 DC8-OMI = RMS = 1.18 Results (and regression) are influenced by one outlier

Outlier with outlier without r DC8-OMI RMS Regressiony= xy= x Standard procedure for extrapolating DC 8 profile to surface (level seen by OMI) introduced large uncertainty for outlier point

Statistical analysis Take differences of individual OMI pixels with matching DC8 column 128 OMI pixels Center Gaussian = Width Gaussian = 0.59 Outlier

DC8 vs. GEOS-CHEM profiles n = 29 DC8 data binned to GEOS-CHEM vertical grid GEOS-CHEM sampled at flight time No extrapolation needed

DC8 vs. GEOS-CHEM profiles Only profiles over land

DC8 vs. GEOS-CHEM profiles Only profiles over ocean

DC8 vs. GEOS-CHEM profiles Outflow profiles: Away from Houston, Mexico City Enhanced OMI NO2 column values Flight reports

DC8 vs. GEOS-CHEM columns Outflow columns: Away from Houston, Mexico City Enhanced OMI NO2 column values Flight reports r = 0.59 n = 29 DC8-GEOS = RMS = 1.38 No vertical extrapolation difficulties Spatial representativity difficulties

OMI vs. GEOS-CHEM columns Figure(s) suggests: Overall patterns (land-sea, hotspot-downwind) are ‘captured’ Source regions may be biased, plumes misrepresented 3-way comparison… To do/doing: Compare patterns (in space, time) of OMI and GEOS-CHEM trop. NO2 Extend validation analysis to SCIAMACHY NO2

OMNO2 Data Verification Method: Run “CAMA” software (Sneep et al.) to check general behaviour, swath dependence, and correlations between parameters Not possible for NRT data format Runs for 2005, either all or 1000 orbit blocks 1.all data – check for viewing angle dependence 2.As 1, but less than 30% clouds 3.As 2, but descending removed (AM) 4.China, high tropospheric NO2 only

Total & tropospheric NO 2 (2005 average, 5316 orbits) Total NO 2 Tropospheric NO 2 Ascending orbits only

Total & tropospheric NO 2 (JFM 2005, orbits ) Total NO 2 Tropospheric NO 2 All orbits Total NO2 Tropospheric NO2

Total & tropospheric NO 2 (JFM 2005, orbits ) Total NO2 Values too high in descending part of orbit Tropospheric NO2 Ascending orbits

Total & tropospheric NO 2 (JFM 2005, orbits ) Total NO2 Tropospheric NO2 Ascending orbits

Latitude & solar zenith angle (2005 average, 5316 orbits, all data) Along-track averages of all OMI pixels in 2005 (all cloud fractions, ascending and descending) Solar zenith angle latitude

Cross-track tropospheric NO2 (2005 average, 5316 orbits, all data) Total NO 2 Tropospheric NO 2 Conclusion: No strong viewing angle dependence West side swath lower NO2?

Correlations tropospheric NO2 and other parameters Other results: NO2 stratosphere and unpolluted very well correlated (straight line) NO2 total and tropospheric almost straight line Polluted area (China) JFM 2005

Correlations total NO2 and other parameters Correlations with sza, total scatter angle, OMTO3 Refl orbit average Late March 2005

Correlations tropospheric NO2 and other parameters Correlations with sza, total scatter angle, OMTO3 Refl orbit average Late March 2005

Correlations total NO2 with ozone 100 orbit average Late March 2005

Outlook Investigate further using CAMA Zoom in to interesting regions Suggestions welcome!