In 2007, China required some coal power plants to install Continuous Emissions Monitoring Systems (CEMS) to track pollutants given off by those stations. In 2014, the Chinese government implemented tighter emissions standards for coal plants. Have those two regulations worked to reduce pollution?

The answer is yes, but with a few caveats.

In a paper published last week, researchers compared troves of CEMS readings to emissions readings from a NASA-owned satellite. They found that while Chinese regulations definitely lowered sulfur dioxide (SO 2 ) levels, there's some evidence that CEMS data shows an overly rosy picture of how large the drop was. Coal plants in key regions were given tighter standards than those elsewhere, and those plants facing tighter standards appeared to miss their targets more often than not.

Global implications

China is a major user of coal and therefore a major contributor to climate change. (Its per-capita coal emissions are less than those of the US, however.) The country's coal use had been on the decline since 2013, according to the Brookings Institution, but 2017 saw an increase, driven by increased economic activity in the first half of the year. Though initially it had been reported that Chinese coal use increased by about three percent, Brookings contends that the increase was probably a more modest one percent.

The Chinese government has seemed to take the risks of climate change seriously—it has invested significantly in solar and wind installations, and it has taken small steps to implementing a cap-and-trade system. Still, verifying that its coal plants are using appropriate emissions controls is important because those coal plants are likely to be used for decades to come. In a best-case scenario, identifying which coal plants are likely cheating on their emissions targets can help Chinese regulators design better enforcement.

Lesser-watched pollutant

The researchers, from MIT and Colorado University Boulder, chose to focus on SO 2 emissions readings. SO 2 is a major pollutant that can cause a number of health issues, and an excessive amount in the atmosphere can cause acid rain.

According to CEMS data, SO 2 emissions per plant decreased by an average of 13.9 percent after the Chinese government instituted stricter standards for coal power plants. But the CEMS data sometimes had missing readings, which could have hidden hours of operation in which the power plant operator knew it could not satisfy the new standards. To test for poor-performance omissions, the MIT and CU Boulder researchers used satellite data to confirm the decrease in SO 2 emissions.

The satellite data could only be used for a small subset of the coal plants that were indexed, because the researchers didn't want emissions sources other than coal-fired power plants to influence the data. That subset consisted only of those power plants that produced 50 percent or more of the power generation in a 35km area. In non-key areas where standards were more lax, the satellite readings were closer to the CEMS data. In key areas where standards were stricter, the CEMS data was considerably better than actual readings. The researchers controlled for any other SO 2 -producing industry that could be in the area, so they were able to rule out those effects.

Instead, the researchers offer another explanation: "Penalties for falsifying data have historically been lower than those for violating the standard." This suggests it's sometimes cheaper to provide bad data and see if you get away with it than it is to get caught with bad numbers at the time of posting. Guidance on reporting CEMS data has also been thin, the researchers noted, so it's harder for enforcement officials to tell if numbers have been misreported.

"Our findings based on the satellite comparison further suggest that manipulation is far from universal but may have increased as compliance grew more costly or difficult," the authors state.

To stamp out data manipulation, the authors suggest that China could make penalties for data falsification more painful. Another alternative, they say, goes back to the cap-and-trade system that the country has been exploring. Emissions trading systems would allow for flexibility because plants that can reduce emissions efficiently have a market incentive to do so, and plants that can't reduce emissions efficiently have the flexibility to buy credits on the trading system and can keep emitting. "However, for these systems to work, high-quality emissions reporting is essential," the paper states.

PNAS, 2018. DOI: http://www.pnas.org/cgi/doi/10.1073/pnas.1800605115 (About DOIs).