Incorrect policy interpretation affects conclusion on SO2 emissions by coal-fired power plants in China.

Karplus et al. (1) raise the concern of potential data manipulation by coal-fired power plants in China by comparing Continuous Emissions Monitoring Systems (CEMS) data with NASA satellite data. Since the two sources of data are not directly comparable, the comparison in the paper is empowered by a policy shock assumed to occur on July 1, 2014, when a new emission standard (GB13223-2011) was set to reduce SO2 emissions from coal power plants. Ideally, this shock isolates the changes in SO2 emissions as a result of the new emission standard in both the CEMS and NASA data, creating a correspondence between the two. However, Karplus … [↵][1]1To whom correspondence should be addressed. Email: changgui.dong{at}ruc.edu.cn. [1]: #xref-corresp-1-1