Union Environment Minister Prakash Javadekar on Thursday said the government's efforts to control air pollution have led to a decrease in the number of days with 'poor' air quality in the national capital region (NCR) by about 50 per cent in the last four years.Speaking at an event here to mark World Environment Day that falls on June 5, he said steps such as setting up air quality monitoring centres across the country, bringing better vehicular emission standards and controlling waste and stubble burning have shown positive results."In 2014, there were 300 days in 'poor' category. In 2017, the number reduced to 213 and in 2018 to 206. We are sure that it will be below 200 this year," Javadekar said without quoting any source for the information.Days with 'moderate to good' air quality increased from 108 in 2016 to 159 in 2018, he said.Urging everyone to come together to solve the issue of air pollution, the Minister said: "Wearing a mask alone would not help. We need to change our behaviour."