The ADB said that poor air quality had reached such a serious level that it was "jeopardising health and sustainable growth".
The loan is intended to cut the region's coal use, among other pollution issues.
China is the world's biggest polluter.
The
loan will target Beijing city and surrounding areas including Hebie and
Tianjin. The region is home to more than 100 million people and
accounts for 10% of China's gross domestic product, the ADB said.
