By Michael Bristow
BBC News, Kunming
China has begun an ambitious project to survey the country's major sources of pollution.
Beijing hopes the survey will give a clear picture of pollution in China
Factories, farms and other polluters will have to declare how much, and what kind of pollutants, they discharge.
The government admits it will be difficult to get companies to supply accurate data, so it is offering them immunity from fines and prosecution.
But even with this incentive, some say the system has flaws which will make it difficult to get accurate information.
Companies across the country are currently being asked to provide information for the China Pollution Source Census, which will be published next year.
In an interview with the BBC, Wang Yuqing, the man in charge of the project, said the main aim was to get a clear picture of China's pollution problem.
The government will then use the information to develop new policies, he said.
Mr Wang added that the government would not use the information it collects against polluting firms.
"It is not about punishing or fining any particular company," he said on the sidelines of a meeting about the census in Kunming, Yunnan Province.
'No turning point'
But getting a clear picture could be difficult, as companies are being asked to supply their own pollution data.
Officials are concerned that some firms will cover up the amount of pollutants they discharge.
There are concerns some businesses could cover up data
Census officials have already set up a hotline so people can phone in and expose firms supplying false information.
Mr Wang said companies will be punished if they do not report accurate data.
Ma Jun, of the Beijing-based Institute of Public and Environmental Affairs, said the government census was a good idea.
But he added: "We need reliable date and, at the moment, there are obvious gaps."
The institute he works for has a list of 15,000 polluting businesses in China, compiled from information released by the government.
That list is getting longer all the time.
"On the pollution situation, we have seen improvements, but we haven't got to the turning point yet," he said.