Lok Lamsal, Nickolay Krotkov, Sergey Marchenko, Edward Celarier, William Swartz, Wenhan Qin, Alexander Vasilkov, Eric Bucsela, Dave Haffner 19 th OMI Science Team Meeting KNMI, De Bilt August 31, 2015 Improvement of NASA Operational OMI NO 2 Retrievals Overview 1. There are issues with the current (version 2) NO 2 slant column density (SCD) retrievals; 2. Resolution and emissions of model NO 2 profiles used in retrievals are important; 3. Surface reflectivity has significant impact on NO 2 retrievals Next talk by Sergey Marchenko Talk by Alexander Vasilkov at 3:20 PM 3)De-striping 4)Strat-trop separation 3)De-striping 4)Strat-trop separation 1) Spectral fit (DOAS) 1) Spectral fit (DOAS) 2)RTM NO 2 and T profiles Reflectivity Cloud fraction/pressure Aerosols Surface pressure Viewing geometry AM F NO 2 SCD NO 2 tropospheric VCD NO 2 stratospheric VCD Retrieval Scheme for OMI Stratospheric and Tropospheric NO 2 V2 validation: OMI strat NO 2 higher than other measurements Krotkov et al., 2012 (Aura Science Team Meeting) Goddard SCD: Algorithm from scratch, thoroughly evaluated, data available for entire 2005 and few months from other years (Next talk by Sergey Marchenko) Marchenko et al., 2015, JGR New KNMI SCD: Modification in existing algorithm van Geffen et al., 2015, AMT NO 2 Slant Column Densities (SCDs): Development Current version (V2) DOMINO (KNMI) SCD (KNMI) OMNO2A OMNO2 (Goddard) Next version (V3) DOMINO (KNMI) SCD (Goddard) OMNO2 (Goddard) SCD (KNMI) V2.0 SCD (OMNO2A & DOMINO) Goddard SCD Orbit March 20, 2005 % Difference (Goddard - V2.0 SCD ) Goddard SCDs are 10-45% Lower Than Current V2.0 SCDs, and Have Reduced Striping Orbit March 20, 2005 V2.0 SCD (10 15 molec. cm -2 ) Goddard SCD (10 15 molec. cm -2 ) Ratio (Goddard/V2.0 SCD) V2.0 SCD (10 15 molec. cm -2 ) Difference (Goddard-V2.0 SCD) Relative difference Absolute difference SCD Difference Has Both Additive and Multiplicative Components Most SCD Bias Ends up in the Stratospheric Estimates (Goddard SCD) March 20, 2005 % Difference in stratospheric NO 2 (Goddard-V2.0) Stratospheric NO 2 based on Goddard SCDs are 20-35% lower (vs V2.0 data), and are in better agreement with SCIAMACHY/GOME-2 results. SCD Bias also Affects Tropospheric Retrievals (Goddard SCD) March 20, 2005 Difference in tropospheric NO 2 (Goddard-V2.0) % Difference in trop NO 2 (Goddard-V2.0) Goddard trop NO 2 (10 15 molec. cm -2 ) Tropospheric NO 2 based on Goddard SCDs are 10-25% lower (vs V2.0 data), and the difference varies with column amount Sensitivity of AMF to A-Priori NO 2 Profiles: Spatial Resolution We have generated monthly NO 2 profiles for each year from a high resolution (11.25) GMI global simulation with year-specific emissions. A factor of 4 increase in resolution changes retrievals by up to 15% in some locations. GMI, June, 2005 sza=45, vza=30, raz=45 (AMF 2x2.5 AMF 1x1.25 )/AMF 1x1.25 2x2.5 1x1.25 Sensitivity of AMF to A-Priori NO 2 Profiles: Emission Inventory OMI NO 2 (2010 July) Retrievals w/ 2005 profilesRetrievals w/ 2010 profiles ABA / B Profiles based on outdated emissions can introduce significant retrieval errors overestimation where emissions have reduced and underestimation where emissions have increased. Lamsal et al., 2015 (Atmos. Env.) Sensitivity of AMF to A-Priori NO 2 Profiles: Improvement in Accuracy of Estimated Trends If profiles used in retrievals are based on outdated (and constant) emissions, they could affect trends by 1-2%/year (e.g. over USA). GMI simulation for June, 2005 (AMF NoL AMF L )/AMF L sza=45, vza=30, raz=45 Sensitivity of AMF to A-Priori NO 2 Profiles: Lightning NO x Neglecting lightning NO x changes profiles, AMFs, and therefore VCDs Some users (e.g. BEHR product) recalculate AMF using high-resolution regional model profiles that may not include lightning NO x emissions.What errors might they introduce in the data they generate? Sensitivity of AMF to Surface Reflectivity 0.01 change in surface reflectivity can change retrieval by 2-20%. Changes are larger for low reflective surface and high NO 2 levels. GMI, June, 2005 Eastern US sza=45, vza=30, raz=45 Polluted Moderate Unpolluted % change in AMF for 0.01 change in reflectivity % AMF & Surface Reflectivity: Issues OMI operational NO 2 algorithms use surface LER climatology from Kleipool et al., Coarse resolution (0.50.5), Cloud and aerosol contaminations Regional scientific studies/products using high resolution MODIS products (All limited over land) StudiesReflectivity type (MODIS) Modification in cloud and aerosols? Russell et al., 2011 (BEHR) BSA as LERNo Zhou et al, 2012BSA, WSA, BRF as LER also, Complete BRDF model No Lin et al., 2015 (POMINO, Dalhouse AMF) Complete BRDF modelYes AMF & Surface Reflectivity: Our Approach Talk by Alexander Vasilkov OMI MODIS (Land only) BRDF Model Geometry VLIDORT (V2.7) Land LER Ocean LER LER R = TOA radiance R 0 = Path scattering reflectance of atm T = Atmospheric transmittance S = Spherical albedo of atmosphere Cox-Munk + Water Leaving Radiance Model AMF & Surface Reflectivity: LER Comparison OMI orbit (November 13, 2006) OMI LER Kleipool et al, 2008 MODIS-derived LER Difference (MODIS OMI LER) Cloud? Sun glint LER changes due to angles Preliminary AMF & Surface Reflectivity: Effect on AMF Preliminary OMI orbit (November 13, 2006) Difference (MODIS OMI) Changes in AMF with MODIS-based LER within 20%; smaller than previously reported. Future Plans Release of new version (V3) of OMNO2 early next year; Version 3 will include new Goddard SCD and high-resolution NO 2 profiles from GMI with year-specific emissions; Continue working on MODIS-based reflectivity, aerosols, and fully coupled NO 2 and cloud retrievals for a longer term plan. Acknowledgment NASA Earth Science Division for funding of OMI NO 2 product development U.S. Aura operation and OMI SIPS processing teams KNMI OMI team Extra Slides July average NO 2 profiles for 3 PM local time (DISCOVER-AQ, Maryland, 2011) Surface reflectivities: 0.1 to 0.15 at 0.01 steps Solar zenith angles: 10 to 85 at 5 steps Aerosol optical depths: 0.1 to 0.9 at 0.1 steps AMF & A-Priori NO 2 Profiles: Mixing Scheme & PBL Heights Errors in PBL heights and differences in mixing scheme can lead to errors of up to 25%. Model profiles should be based on more accurate mixing scheme and PBL heights. Slant column NO 2 retrievals by spectral fitting using DOAS New DOMINO SCDGoddard SCD % Difference (Goddard SCD - SCD) Courtesy: KNMI NO 2 team for new DOMINO SCD AMF & Surface Reflectivity: Sensitivity AMF & Surface Reflectivity: Our Approach OMI MODIS (MCD43GF) BRDF coeff (f iso, f vol, f geo ) 30 arc sec, 8-day, gap-filled Pixel corners VLIDORT (V2.7) RossThick-LiSparse Cox-Munk Water leaving Land LER Ocean LER LER R = TOA radiance R 0 = Path scattering reflectance of atm T = Atmospheric transmittance S = Spherical albedo of atmosphere Talk by Alexander Vasilkov