BEIJING - Emissions from motor vehicles have become the major source of air pollution in China's large and medium sized cities, according to a report issued Thursday by the Ministry of Environmental Protection.

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According to the annual report on prevention and control of vehicle pollution, the volume of pollutants generated by motor vehicles across China in 2009 amounted to 51.4 million tons, with cars contributing most of it.

In a second statement issued along with the report, one-third of 113 major cities failed the air quality test in 2009.

Meanwhile, acid rain and smog have occurred so frequently in certain regions of China that some areas were shrouded in smog for 200 days during the year. Vehicle emissions should be blamed for much of this smog, according to the statement.

The report also noted that in 2009 the number of cars owned by Chinese citizens jumped to 170 million, a 9.3 percent increase year on year, and 25 times car ownership figures in 1980.

The statement reads, as car ownership swells, it will add more pressure on air pollution control agencies in these cities.

However, the report also showed that the emission of pollutants had been growing, but at a lower rate since 2000, which should be attributed to efforts to phase out high-emission vehicles.