Excessive emission of pollutants from factories, dust pollution and straw burning may have caused smoggy days in October in Beijing, Tianjin and Hebei province, the Ministry of Environmental Protection said on Monday.

The ministry carried out an inspection campaign with local environmental protection bureaus in Beijing, Tianjin and Hebei in October to curb illegal behavior affecting environmental protection.

Fourteen of 65 companies and factories checked had illegal behavior affecting environmental protection, such as excess emission of pollutants, and 15 had problems in environment management.

In Tangshan, Hebei province, five enterprises were punished for their pollution, including one that had production suspended.

Dust pollution also worsened air pollution in the region with no effective dust-proof measures taken in construction sites, coal yards and rubbish dumps.

The campaign will continue every month from October in Beijing, Tianjin and Hebei to help local authorities control air pollution.

The inspections also target areas including the Yangtze and Pearl River Delta regions, as well as Liaoning and Hunan provinces, according to the ministry. Media are invited to participate in the inspections.

The government aims to cut the density of inhalable particulate matter by at least 10 percent in major cities by 2017.

PM2.5, a key indicator of air pollution, should fall by about 25 percent from 2012 levels in Beijing and surrounding provincial areas by 2017.

The Yangtze and Pearl River Delta regions should see reductions of 20 and 15 percent from 2012 levels over the same period.