Beijing launched carbon emissions trading on Thursday, making it China's third market for compulsory carbon trading. An initial 490 companies, whose carbon emissions account for 40 percent of the city's total emissions, are included in the program, according to the Beijing Municipal Commission of Development and Reform. Companies that produce excessive emissions will be able to buy unused quotas on the market from companies that cause less pollution. On Tuesday, Shanghai launched its compulsory carbon trading market, the country's second such market, and Shenzhen in Guangdong province started its market in June.