Environment Minister Imran Hussain on Tuesday said the city's air quality may worsen and directed to continue measures to impound and shut down visibly polluting vehicles and factories.Hussain, in a letter to Environment Department Secretary Keshav Chandra, said the air quality has improved, but it would be temporary and may worsen in the coming days according to reports.The Minister directed Chandra to continue a slew of measures, including mechanised sweeping and vacuum cleaning of roads, throughout the winter season.The other steps include spraying of water to reduce dust de-suspension, avoid or minimise manual brooming, impounding of visibly polluting vehicles, and closing down of polluting factories among others."Non-biomass heating facility must be provided at 'Rain Baseras' (night shelters) and such facilities," one of the steps read."Use of firecrackers must be stopped, the owner of the premises will be responsible for violation," another step said.