Satellite measurements oversee China's sulfur dioxide emission reductions from coal-fired power plants

To evaluate the real reductions in sulfur dioxide (SO₂) emissions from coal-fired power plants in China, Ozone Monitoring Instrument (OMI) remote sensing SO₂ columns were used to inversely model the SO₂ emission burdens surrounding 26 isolated power plants before and after the effective operation of their flue gas desulfurization (FGD) facilities. An improved two-dimensional Gaussian fitting method was developed to estimate SO₂ burdens under complex background conditions, by using the accurate local background columns and the customized fitting domains for each target source. The OMI-derived SO₂ burdens before effective FGD operation were correlated well with the bottom-up emission estimates (R = 0.92), showing the reliability of the OMI-derived SO₂ burdens as a linear indicator of the associated source strength. OMI observations indicated that the average lag time period between installation and effective operation of FGD facilities at these 26 power plants was around 2 years, and no FGD facilities have actually operated before the year 2008. The OMI estimated average SO₂ removal equivalence (56.0%) was substantially lower than the official report (74.6%) for these 26 power plants. Therefore, it has been concluded that the real reductions of SO₂ emissions in China associated with the FGD facilities at coal-fired power plants were considerably diminished in the context of the current weak supervision measures. (letter)