NEW DELHI: Mumbai, touted to have considerably cleaner air than most north Indian cities , has been recording far higher air pollution levels than Delhi for over two weeks now.The reason, surprisingly, may not be a sudden increase in Mumbai's emissions but a sharp improvement in Delhi's air quality , scientists said.The System of Air Quality and Weather Forecasting and Research (SAFAR), under the Indian Institute of Tropical Meteorology, assessed the air quality in the two cities, as well as Pune, between February 27 and March 13, 2017.Mumbai recorded 13% "satisfactory" days, Delhi 40% and Pune 47%. In Mumbai, 20% of the days had "very poor" air quality while Delhi had none.