Vehicles are the biggest polluters in Beijing, Hangzhou, Guangzhou and Shenzhen.

　　Coal-burning emits the most particulates in Shijiazhuang and Nanjing.

　　Tianjin is mostly troubled by airborne dust, while in Ningbo, it is industrial production.

　　In Shanghai so-called "mobile sources", including ships, are said to be responsible for most of the pollution.

　　大气污染来自汽车尾气

　　The research program was initiated and led by the Ministry of Environmental Protection two years ago.

　　Hai Yin is an official with the Ministry's Environment Monitoring Department.

　　"We selected nine cities in Beijing-Tianjin-Hebei area, Yangtze River Delta and Zhujiang River Delta, as they tend to have a lot in common. Firstly, they have a good technology background for conducting this kind of researches. Secondly, historically speaking, pollution in these cities is relatively heavier than other cities. And thirdly, the cities themselves have conducted their own research into pollutants such as PM10, which laid a good foundation for our additional research."

　　The new analysis is meant to try to provide local officials with information as to how to better manage air pollution.

　　As an example, the results for Shanghai suggest municipal officials should focus not only on vehicles, but also the city's shipping industry, both domestically and internationally.

　　Luo Hailin is with Shanghai's environmental protection bureau.

　　"There are a lot of opportunities for Shanghai to tackle 'mobile sources.' Authorities should be better controlling so-called yellow-labeled vehicles. As for the ships, it hasn't been our priority in the past. But now it seems they have a considerable impact on the environment. Moreover, another issue is the trucks. Generally speaking, the number of vehicles in Shanghai is less than that of Beijing. However, our calculations show the pollution levels from this category are almost the same in the two cities. The main reason is Shanghai is home to more trucks."

　　Yellow-labeled vehicles refer to those whose exhaust emissions are below national standards.

　　Beijing's municipal authorities already laid out an updated emergency plan for heavy pollution days this week.

　　If heavy smog lingers for more than three days, a top-level emergency plan will go into effect to reduce emissions, including limiting the use of private vehicles.

　　Apart from the nine cities in the latest analysis, another batch of 26 cities will have their main sources of pollution disclosed later this year.

　　The findings are said to be just the first step towards a broader pollution management plan for China.

　　The next step will see researchers take a 'bigger picture' look at atmospheric pollution on a regional level.

　　For CRI, I'm Qi Zhi.