Carbon emissions from cars in the Chinese city of Chengdu could be underestimated by more than half under conventional testing methods, according to the preliminary results of a study released on Wednesday.
The findings from the study in the central city were supported by a research arm of China's top planning body using data from Uber and taxi firms.
It found that standard laboratory estimates of carbon emissions from cars were off by about 6,500 metric tonnes per day, or about 59 percent.
The study aims to pave the way for more targeted carbon emissions policies in China.
"In the (the Chinese government's most recent) 13th five-year plan, every region and city has the target, but the question is how you meet those targets and how do you verify the target has been met?" said An Feng, head of the Innovation Center for Energy and Transportation, a think-tank that led the study.
"You cannot manage if you can't measure it."
Vehicles emissions have previously been far more difficult to measure than fixed sources of pollution such as factories and power plants.
Using data from ride-hailing services and taxis would be better than current laboratory testing arrangements in preventing manipulation by local governments and automakers, An told Reuters in an interview prior to the summit.
To expand from ride hailing and taxis to all cars, the Chinese government would need to find an arrangement with automakers to gather data from private cars, although while also addressing privacy and security concerns, he said.
An said he envisions the study expanding around China so that cities, and eventually even companies, can be ranked by carbon emissions.
Systems and policies could then be tailored to this data, such as taxing companies or even products based on the amount of carbon they create.