Delhi has witnessed significant ozone build-up this summer, adding to the public health risk -- shows a latest analysis done by Centre for Science and Environment (CSE). Building up to the World Environment Day, CSE has analysed the real-time air quality data available from the key monitoring locations of Delhi Pollution Control Committee for the summer months of 2016 and 2017. This shows ozone pollution in the city is worsening progressively with the onset of summer.