In China, the country leading the world in electric vehicle sales, problems with smog have forced officials to shut down major cities to protect residents in recent months. With air quality issues front and center, there has been a boom in sales of plug-in hybrids and EVs, much of it powered by government incentives. Yet this shift to greener vehicles may not help the cause. Data about China’s coal-heavy electric grid now has researchers concerned air pollution will get worse from plug-in car adoption.

When describing cars as zero emissions vehicles (ZEVs), the only element guaranteed to be carbon-free is the vehicle during operation. It takes a zero-emissions power source (e.g., wind, solar, or hydro) to make the system a truly clean transportation alternative. That’s not the case in China, where the percentage of renewables in the energy mix remains pitifully small, with Reuters reporting a grid running on 90% coal in Beijing and Tianjin, two major cities with EV initiatives in place.

As a result, the rapid adoption of plug-in vehicles could make China’s air quality worse in the short term. Reuters reports Tsinghua University researchers found electric vehicles are producing two-to-five times the amount of particulate matter and chemicals that gasoline cars do. In effect, China is swapping gas cars for coal cars.

The situation will not improve until China makes major headway in the amount of renewables powering the electric grid, something the country is attempting with big investments in solar and wind infrastructure. Yet it is difficult to have much hope in green energy initiatives when four new coal plants are opening every week, as the CBC reported in December. Equally distressing are reports China is burning much more coal than officials are allowing on the public record.

According to a New York Times article from November 2015, China was burning 17% more coal than the government had reported in previous years. For the world’s largest producer of emissions from coal products, that extra amount turned out to be massive, itself 70% more than the U.S. produces in a year. Though the electricity grid was one of the least affected sectors, issues with transparency and accountability remain huge factors in the country’s energy policy.

Issues surrounding power sources for the grid have dogged the electric vehicle industry for years. In fact, the easiest way to call into question the benefits of EVs is to point to dirty power sources. For U.S. green car adopters, the issue has been settled. Research by The Union of Concerned Scientists showed plug-in vehicles have environmental benefits in every region of the U.S., with the best areas for renewable power matching up to the areas of highest EV concentration. From production to the end of their useful lives, electric cars in the U.S. produce half the emissions of gasoline cars.

As for the increase in zero-tailpipe-emissions vehicles on the road in major Chinese cities, it is unclear if less pollution during vehicle operation will help reduce smog concentration in Beijing and other cities. Taken as a national energy policy, powering cars on over 90% coal is several steps in the wrong direction, and the air may get worse before it gets better. Once the grid gets cleaned up, that electric car boom can start paying actual dividends for the Chinese people.

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