A day after Delhi's air quality plunged to the 'severe' category, Environment Minister Gopal Rai on Thursday said strict pollution control measures would be enforced if the conditions worsened. Rai also attributed the worsening air quality to a combination of calm winds and a drop in temperature that caused the pollutants to remain trapped in the air. The national capital's Air Quality Index (AQI) at 9 am remained in the 'severe' category, with a reading of 428. On Wednesday, Delhi reported the worst AQI in the country, with the air quality turning 'severe' for the first time this season. Rai said at a press conference that there had been a change in the weather pattern during the past two days. Wind speeds are expected to pick up between Friday and Saturday, reaching six to 12 kilometres per hour and that should help reduce pollution levels, he said. Regarding the implementation of pollution mitigation measures under GRAP III, the minister said it would not be imposed yet as the