SHANGHAI - Growth in Chinese auto sales slowed to 8.2 percent on-year in July, traditionally a slack season in the world’s largest car market, an industry group said Thursday. Total vehicle sales were around 1.38 million vehicles, the China Association of Automobile Manufacturers said in a statement. In comparison, China’s auto sales rose 9.9 percent year-on-year in June to 1.58 million units, previous figures showed. The nation’s auto sales began to slow last year after the government rolled back buying incentives and some cities imposed tough restrictions on car numbers to ease chronic traffic congestion and pollution. Just last month, the southern city of Guangzhou set rules to limit the number of cars through a quota on the number of vehicle number plates made available by the government. China’s overall vehicle sales rose just 2.5 percent to 18.51 million units in 2011, compared with an annual increase of more than 32 percent in 2010. For the first seven months of the year, auto sales rose 3.6 percent to 10.98 million vehicles, the association said.