The Delhi government has urged Haryana to allow only BS VI-compliant buses to enter the national capital from October 1 in order to help control air pollution in the city. The request was made to deal with the problem of vehicular pollution in the city, which officials here indicated, is contributed to in part by vehicles coming from the neighbouring state of Haryana. The national capital witnesses high levels of air pollution in the winter months from October due to a multitude of factors including stubble burning and vehicular traffic.