China’s Guangdong province sold 3 million metric tons of carbon emission permits for 180 million yuan ($30 million) in its first auction on Monday, the first of its kind in China, Bloomberg reports.

Guangdong is the world’s second-biggest carbon market and the largest of seven such markets planned for China. It’s the first region to use carbon auctions to allocate emissions permits instead of giving them away for free.

Earlier this month Beijing became the third Chinese city to launch a carbon trading program.

China has a strong policy framework in place to transition to a green economy, but significant challenges — including pollution problems — stand in the way, according to a study sponsored by the United Nations Environment Programme and the Chinese Ministry of Environmental Protection.