1. OMI Science Team Meeting 24 – 27 June 2008, FMI Iterative Retrieval of Large SO 2 from Volcanic Eruptions Kai Yang 1,3, Nikolay Krotkov 1,3, Arlin Krueger 2, Simon Carn 2 Pawn K. Bhartia 3 1 GEST, UMBC, Baltimore, MD, USA 2 JCET, UMBC, Baltimore, MD, USA 3 GSFC, NASA, Greenbelt, MD, USA

2. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Detect and Quantify SO 2

3. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 SO 2 Algorithms Retrieval Challenge: Wide range of loadings and vertical distributions Existing Algorithms: Band Residual Difference (BRD) method Linear Fit (LF) method Both methods are used in making OMI NRT and operational OMSO2 products. Improvements in addressing these two questions: How small can OMI see? How large can OMI measure?

4. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Profile shapes: O 3 ( Ω ) uses V8 climatology, SO 2 ( Ξ ) uses Gaussian specified by a central height and a width. Initial guess: latitude based O 3 guess or an adjacent pixel O 3 value, no SO 2, derive MLER cloud fraction ( F c ) at λ=333 nm, using OMCLDRR cloud pressure. Iterative Spectral Fitting (ISF) Method: Combo O 3 and SO 2 Retrievals

5. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Sample Results: Eruption of Sierra Negra 10/22/2005 10/23/2005

6. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Sierra Negra Eruption 10/23/2005 OMI Retrievals: ISF vs. LF ISF SO 2 Mass LF SO 2 Mass 1740 kilotons 950 kilotons (-45%)

7. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Largest SO 2 Pixel Value Orange: lava flows Aqua MODIS Bands 7, 2, 1 Composite

8. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Ozone Consistency: Inside and Outside of the Plume Along track plots of O 3 and SO 2 (Along track)

9. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Ozone Consistency: Inside and Outside of the Plume Maps of O 3 : ISF vs. LF

10. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 How Good are ISF Retrievals? High SO 2 Fitting Residuals 1 N-value = -2.3% Radiance Window = 317.85–333.00 nm Error = 0.58 %

11. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 High Precision Fitting Medium SO 2 Low SO 2 Fitting Error = 0.25% Fitting Error = 0.15% Background SO 2 Fitting Error = 0.14%

12. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 SO 2 Vertical Distribution Assumed profile too low Imeas<Iassum at short λ Simulated Retrievals Assumed profile too high Imeas>Iassum at short λ

13. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Improving Retrieval Accuracy: Adjusting SO 2 Central Height

14. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Improving Retrieval Accuracy: Adjusting SO 2 Central Height

15. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Comparison with AIRS SO 2 SO 2 central height

16. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Anatahan Eruption: 04/06/05 Iterative Spectral Fit Linear Fit: OMSO2 TRM Derived SO2 central height ≈ 10.5 KM Assumed Central height = 7. 5 KM

17. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Anatahan Eruption: 04/06/05 OMI – AIRS Comparison Iterative Spectral Fit AIRS ΔBT

18. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Anatahan Eruption: 04/06/05 Aerosol Index Iterative Spectral Fit OMTO3 Linear Fit, OMSO2 Terra MODIS

19. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Nyamuragira Eruption:11/28/06 SO 2 & Aerosol Index ISF SO 2 ISF AI OMTO3 AIOMSO2 AI

20. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Height & Distance Nyamuragira, DR Congo Nov 28 – Dec 04, 2006 SO 2 Plume height ~ 7 KM Sierra Negra, Galápagos Islands Oct 23 – Nov 01, 2005 SO 2 Plume height ~ 3 KM

21. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Height & Distance Soufriere Hills, Montserrat, West Indies May 20 – June 11, 2006 SO 2 Plume height ~ 13 KM on May 20 Distance tracked ~ 20000 KM

22. K. Yang, GEST UMBC & GSFC NASA 13 th OMI Science Team Meeting, FMI, 24 – 27 June 2008 Summary Operational OMSO2 products tend to underestimate SO 2 column amounts, more so when they are large ( > 50 DU). New algorithm provides more consistent ozone values inside and outside of volcanic plumes, and more precise SO 2 columns. Record SO 2 column retrieved. OMI UV2 measurements contain SO 2 vertical distribution info. Derived central plume heights are consistent with near simultaneous AIRS observations. The slope of theF c -λ curve yielded from the fitting algorithm may be used as a better aerosol index.