retrieval of vertical columns of sulfur dioxide from sciamachy and omi: air mass factor algorithm...
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Retrieval of Vertical Columns of Sulfur Dioxide from SCIAMACHY and OMI: Air Mass Factor Algorithm Development, Validation, and Error
AnalysisChulkyu Lee1, Randall V. Martin1,2, Aaron van Donkelaar1, Gray O’Byrne1, Nickolay Krotkov3, Andreas Richter4, Greg Huey5, and John S. Holloway6
1Department of Physics and Atmospheric Science, Dalhousie Univ., Canada; 2Harvard-Smithsonian Center for Astrophysics, USA, 3Goddard Earth Sciences and Technology Center, Univ. of Maryland, USA, 4Institute of Environmental Physics and Remote Sensing, Univ. of Bremen, Germany, 5School of Earth and Atmospheric Sciences, Georgia Institute of Technology, USA, 6NOAA Earth System Research Laboratory, USA
We develop an improved retrieval of sulfur dioxide (SO2) vertical columns from two satellite instruments (SCIAMACHY and OMI) that measure ultraviolet solar backscatter. For each SCIAMACHY and OMI observation, a local air mass factor (AMF) algorithm converts line-of-sight “slant” columns to vertical columns using altitude-dependent scattering weights computed with a radiative transfer model (LIDORT), weighted by relative vertical SO2 profile (shape factor) determined locally with a global atmospheric chemistry model (GEOS-Chem). The scattering weights account for viewing geometry, surface albedo, cloud scattering, absorption by ozone, and scattering and absorption by aerosols. Mean SO2 shape factors simulated with GEOS-Chem and used in the AMF calculation are highly consistent with airborne in situ measurements (INTEX-A and INTEX-B); differences would affect the retrieved SO2 columns by 10%. The retrieved vertical columns are validated with coincident airborne in situ measurements (INTEX-A, INTEX-B, and a campaign over East China). The annual mean AMF errors are estimated to be 35-70% in polluted regions (e.g., East Asia and the eastern US) and less than 10% over clear ocean regions. The overall SO2 error assessment is 45-80% for yearly averages over polluted regions. Seasonal mean SO2 columns retrieved from SCIAMACHY and OMI for 2006 are significantly spatially correlated with those from GEOS-Chem, in particular over the United States (r = 0.85 for SCIAMACHY and 0.82 for OMI). A sensitivity study confirms the sensitivity of SCIAMACHY and OMI to anthropogenic SO2 emissions.
ABSTRACT
Scattering weight
IoIB
Earth Surface
Radiative Transfer Model(LIDORT)
(η) is temperature-dependent cross-section
Calculate ω(η) as function of:• solar and viewing zenith angle (θs, θv)• surface reflectivity• pressure, aerosol• clouds• O3 column:
For individual scenes
1
)()(T
dSAMFColumnsVertical
ColumnsSlantAMF G
Shape factor
SO2 mixing ratio, CSO2(η)
2
)()(SO
airCS
Atmospheric Chemistry Model(GEOS-Chem)
Local AMF Calculation
)(ln)(1
)( B
eG
I
AMF
eta
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dt(η)
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OM
I SO
2 [D
U]
In Situ SO2 [DU]
- - - Reduced major-axis linear fit Y = 1.61X + 0.21 (r = 0.71)
Using constant AMF = 0.36
In Situ SO2 [DU]
- - - Reduced major-axis linear fit Y = 0.95X + 0.05 (r = 0.92)
SC
IAM
AC
HY
SO
2 [D
U]
- - - Reduced major-axis linear fit Y = 1.38X + 0.01 (r = 0.78)
With Old AMF
Using constant AMF = 0.88
- - - Reduced major-axis linear fit Y = 1.12X + 0.06 (r = 0.89)
With New AMF
Cloud Radiance Fraction < 0.2; SZA < 70
GC at OMI overpass within 10% of GC at SCIAMACHY overpass
GEOS-Chem SO2
changes by ×2
OMI SO2 AMFchanges < 30%
Local AMFs improve agreement of OMI and SCIAMACHY with in-situValidation of SO2 vertical columns from SCIAMACHY and OMI with airborne
in-situ measurements for INTEX-A and B (r = 0.9)Validation of GEOS-Chem SO2 shape factors with airborne in-situ
measurements for INTEX-A and B (<10% change in AMF)Large signal from anthropogenic emissions in retrieved SO2 columns
Evaluation of GEOS-Chem Simulation of Shape Factor
Slant Columns with Reference Sector Method
Seasonal Air Mass Factors for 2006
Seasonal Mean Vertical Columns for 2006
Calculated at 313.2 nmCloud Radiance Fraction < 0.2; SZA < 70SCIAMACHY AMF at 319.7 nm within 25%
Local AMF Increases Agreement with INTEX Aircraft Measurements
Summary
Sensitivity of Retrieved SO2 to ΔEmissions
Differences between modeled and measured shape factors would change AMF by <10%
Scatter plots of tropospheric SO2 vertical columns versus those from in-situ measurements during INTEX-A (triangles) and INTEX-B (squares). The constant AMF refers to the OMI operational PBL product. The local AMF is developed here.
Sensitivity of SO2 columns to errors in anthropogenic emissions. The top panel is the difference between GEOS-Chem simulations of SO2 columns using meteorology for 2006 with anthropogenic emissions for 2006 minus one with emissions for 1998. The bottom panel is the difference between OMI SO2 columns for 2006 retrieved using SO2 shape factors from the GEOS-Chem simulations with anthropogenic SO2 emissions for either 2006 or 1998.
Funding: NSERC and NASA