Satellite sensors detected a double digit increase in the number of fields farmers burned after harvesting their crops in early October, the national environmental authority said on Wednesday.

The burning fields contributed to the severe air pollution seen in Beijing in the early part of the week, until winds dispersed the smog on Wednesday evening, the capital’s environment monitoring center said.

Remote monitoring equipment found 376 suspicious field burnings nationwide from Oct 1 to Tuesday, an increase of 16.4 percent over the same period last year, said Zou Shoumin, head of environmental monitoring at the Ministry of Environmental Protection.

Among the hot spots, 220 were found in Central China’s Henan province and another 100 were in Shandong province, another major agricultural region, the ministry said.

Zou said the ministry will conduct regular monitoring on crop burnings and release the results on a daily base on the government website.