An increase in automobile emissions exposed China's Guangdong province to damage from acid rain in the first half of this year, a report found.

The report by the provincial environmental protection department found more than half of the province's 21 cities were polluted by acid rain during that period, China Daily reported Monday.

Most acid rain in the province results from high concentrations of nitrogen oxide and sulfur dioxide in the air, experts said.

Nitrogen oxide in particular has become a problem, a result partly of the greater number of automobiles on the province's roads, the report said.

Industry is also to blame, experts said.

Some cities in Guangdong are burning more coal to produce power because of a decline in power transmission from western China.

All of these factors combine to create a higher level of acid rain, said Zhou Yongzhang, director of the Center for Earth Environment and Resources at the Sun Yat-sen University in Guangzhou.

The most effort should be put into reducing emissions of nitrogen oxides, Zhou said, since regulations are already in place to control the sulfur dioxide released by coal-burning power plants in the province, the manufacturing center of China.