SO₂ Emission Estimates Using OMI SO₂ Retrievals for 2005-2017.

Area of Science:

• Atmospheric Science
• Remote Sensing
• Environmental Monitoring

Background:

• Ozone Monitoring Instrument (OMI) SO2 column densities are crucial for tracking emission trends and identifying emission sources.
• Discrepancies exist among different OMI SO2 retrieval products, necessitating comparative analysis for reliable emission estimates.

Purpose of the Study:

• To evaluate and compare three OMI SO2 retrieval products (NASA SP, NASA prototype, BIRA) for SO2 emission estimation.
• To derive and analyze monthly SO2 emissions using a hybrid inversion method.
• To assess the accuracy and consistency of derived emissions against in situ measurements and existing emission inventories.

Main Methods:

• Employed three OMI SO2 retrieval products: NASA standard (SP), NASA prototype, and BIRA.
• Applied a hybrid 4D-Var/mass balance emission inversion to derive monthly SO2 emissions from NASA SP and BIRA products.
• Compared derived SO2 emissions with HTAPv2 emissions and evaluated posterior GEOS-Chem surface SO2 concentrations against in situ measurements.

Main Results:

• SO2 retrieval consistency is highest under small viewing and solar zenith angles, favoring summer and low-latitude estimates.
• Posterior emission estimates are lower than HTAPv2 in the US, India, and SE China, with differing trends in North China Plain.
• India shows a significant SO2 emission increase (35-48%) from 2005-2016, while China shows a decrease (23-33%) since 2008.
• Posterior GEOS-Chem concentrations reduced model bias in China, US, and India, with BIRA showing better agreement with annual growth rates and spatial variability, and NASA SP with seasonality.

Conclusions:

• The study demonstrates the capability of OMI observations to recover SO2 emissions, highlighting the importance of retrieval product selection and viewing conditions.
• Regional emission trends vary significantly, with India experiencing growth and China a decline in SO2 emissions.
• Both NASA SP and BIRA products provide valuable insights, with BIRA offering better consistency with certain ground-based measurements and NASA SP with seasonality.