TEMPO Aerosols Workshop Near UV aerosol products

1. TEMPO Aerosols Workshop Near UV aerosol products Omar Torres, Changwoo Ahn, Hiren Jethva NASA-Goddard Space Flight Center Greenbelt, MD, 20771, USA September 11, 2017

2. Satellite Aerosol Remote Sensing In aerosol remote sensing, measured reflectances depend on multiple aerosol properties: • Particle size: particle size distribution Fine and coarse modes, std. dev., coarse mode fraction: at least 5 parameters -Particle shape: aspect ratio, 1 parameter -Particle composition: Complex refractive index (wavelength dependent), 2 parameters -Extinction Optical Depth, AOD , 1 parameter • Aerosol vertical distribution (stronger in the UV) Other requirements: -Surface reflectance must be characterized -Cloud-free conditions State-of-the-art satellite aerosol sensors use VIS/near IR observations to retrieve multi-spectral AOD, and Angstrom Exponent, a qualitative indicator of particle size.

3. Use of near UV Satellite Observations for retrieving aerosol properties • Observations in the 340-400 nm range can be used to derive aerosol properties • Advantages: • Low surface albedo at all terrestrial surfaces (.01 to .03 for vegetation; .08 - .12 deserts) • Sensitivity to aerosol absorption. • Negligible gas absorption interference. • Disadvantages: • Ocean color interference • Aerosol absorption detection is aerosol layer height sensitive. • Historically, near UV measurements have been associated with coarse spatial resolution sensors (TOMS, OMI) primarily designed for trace gas retrieval. • At these multi-kilometer resolution sub-pixel cloud contamination (SCC) is the most important error source in aerosol remote sensing. Full exploitation of this retrieval technique awaits the development of high spatial resolution UV instruments that can minimize cloud contamination effects.

4. Improvements in spatial resolution of near UV measurements TEMPO will be, at launch, the highest spatial resolution space borne hyper-spectral sensor ever built

5. Ozone Monitoring Instrument (OMI) An international project: Holland, USA, Finland Nadir solar backscatter spectrometer • 270-500 nm • 13X24 km footprint • 2600 km swath width • Launched on 07-15-04 One of four sensors on the EOS-Aura platform (OMI,MLS,TES, HRDLS) Retrieval Products: Radicals: Column O3, NO2, BrO, OClO O3 profile Tracers: Column SO2 Cloud top pressure Aerosols (OMAERUV) OMI is part of the A-train A global 13-year record of AOD/SSA has been produced from OMI’s near UV observations

6. OMAERUV Retrieval Procedure Level2 calibrated radiances at 354 and 388 nm Surface Albedo (OMI Climatology) Radiative Transfer Calculations Absorbing Aerosol Index -AIRS CO data: Three aerosol types: • Desert Dust • Carbonaceous aerosols • Weakly absorbing Seven aerosol models per type (varying ω0) -Surface Type Aerosol Type Cloud Screening CALIOP Climatology GOCART Climatology Aerosol Layer Height Assumed aerosol parameters: -Particle size distribution -Real comp. refractive index -Relative spectral dep. of imag. refractive index. Inversion Scheme Extinction optical depth Single Scattering Albedo Lookup Tables Plans to apply the OMI near UV algorithm to TEMPO observations are in place.

7. Aerosol Type Determination OMAERUV uses real-time AIRS CO data for aerosol type identification [Torres et al., AMT, 2013] UVAI0 = 0.8 over land UVAI0 = 1.0 over ocean COI = CO /10^18 During TEMPO operation CO measurements will likely be available from CrIS measurements on the S-NPP and JPSS-1 platforms. It may also be available from GeoCARB. The use of TEMPO’s formaldehyde product as smoke tracer is under study.

8. Combined use of OMI and AIRS observations for smoke-dust separation CALIOP OMI AIRS The combined use of AI and CO allows the identification of smoke layers over arid areas on July 7, 2006. - Torres, O., C. Ahn, and Z. Chen, Improvements to the OMI Near UV aerosol algorithm using A-train CALIOP and AIRS observations, Atmos. Meas. Tech., 6, 3257-3270, 2013

9. OMAERUV Retrieval Procedure Level2 calibrated radiances at 354 and 388 nm Surface Albedo (OMI Climatology) Radiative Transfer Calculations Absorbing Aerosol Index -AIRS CO data: Three aerosol types: • Desert Dust • Carbonaceous aerosols • Weakly absorbing Seven aerosol models per type (varying ω0) -Surface Type Aerosol Type Cloud Screening CALIOP Climatology GOCART Climatology Aerosol Layer Height Assumed aerosol parameters: -Particle size distribution -Real comp. refractive index -Relative spectral dep. of imag. refractive index. Inversion Scheme Extinction optical depth Single Scattering Albedo Lookup Tables

10. Cloud Screening Scheme OMI: Pixel-by-pixel basis TEMPO: Spatial Homogeneity At TEMPO’s higher (than OMI’s) spatial resolution, spatial homogeneity analyses can be applied to deal with cloud contamination.

11. OMAERUV Retrieval Procedure Level2 calibrated radiances at 354 and 388 nm Surface Albedo (OMI Climatology) Radiative Transfer Calculations Absorbing Aerosol Index -AIRS CO data: Three aerosol types: • Desert Dust • Carbonaceous aerosols • Weakly absorbing Seven aerosol models per type (varying ω0) -Surface Type Aerosol Type Cloud Screening CALIOP Climatology GOCART Climatology Aerosol Layer Height Assumed aerosol parameters: -Particle size distribution -Real comp. refractive index -Relative spectral dep. of imag. refractive index. Inversion Scheme Extinction optical depth Single Scattering Albedo Lookup Tables

12. CALIOP-based Aerosol Height Climatology OMAERUV uses a CALIOP-based Absorbing Aerosol Layer Height Climatology Torres et al, AMT, 2013 January April Aerosol Layer Height (km) July October

13. Near UV Inversion Scheme 354/388 radiance ratio 388 nm radiance For a given aerosol type and layer height, satellite measured radiances at 354 and 388 nm are associated with a set of AOD and SSA values.

14. AOD Validation With AERONET

17. Summary