As per Greenpeace India, how many Indian metros are hotspots of air pollutant nitrogen oxide?

As per the analysis by environmental Non Governmental Organization (NGO) Greenpeace India, transport and industrial clusters were giving rise to the country's worst Nitrogen Oxide (NOx) hotspots like Delhi, Bengaluru, Mumbai, Kolkata, Chennai and Hyderabad. They have high vehicular population and diesel consumption. The data was collected between February 2018 and May 2019. Coal consumption and industrial clusters like Sonbhadra-Singrauli in Madhya Pradesh and Uttar Pradesh, Korba in Chattisgarh, Talcher in Odisha, Chandrapur in Maharashtra, Mundra in Gujarat and Durgapur in West Bengal were polluting the environment with Nitrogen Oxide emissions.