The impact of traffic on the air quality of Chinese cities has become tremendous, with automobiles being the top air pollution source, says a report released by the Organization for Economic Cooperation and Development (OECD) on Tuesday.

The OECD Report on Environmental Performance Review of China said that in Guangzhou and Shanghai, more than 80 percent of carbon monoxide and 40 percent of nitrogen-oxygen compounds came from automobile emissions.

Carbon monoxide is harmful because it reduces oxygen delivery to the body's organs and tissues. It is most harmful to those who suffer from heart and respiratory diseases. Nitrogen-oxygen compounds are harmful to eyes and the respiratory system.

High levels of the pollutants in air also affected healthy people, said experts.

The report said China should promote the use of clean fuel and environment-friendly vehicles and encourage alternative transport methods.

The OECD and China's State Environmental Protection Administration (SEPA) held a press conference on the publication of the report here on Tuesday.

The report, initiated in 2005, examines the progress made by China since 1990 in air, water and waste management, protection of nature and bio-diversity.

The report pointed out that the biggest obstacles to China's environmental policy implementation are at the local level, because local authorities value economic growth above the environment.

The report urged the Chinese government to increase the effectiveness and efficiency of the implementation of environmental policies and give more supervisory and administrative power to environmental protection departments.

(Xinhua News Agency July 18, 2007)