Global, regional and city scale changes in atmospheric NO 2 with environmental laws and policies

We assess the spatio-temporal changes in global atmospheric nitrogen dioxide (NO2) in its hotspots and 3000 cities with respect to past and current vehicular policies for the period 2002 - 2019. The quantile-quantile (Q-Q) adjustment method is applied to merge the NO2 measurements from different satellites to make the long-term data (2002 - 2019) for this analysis. We find that eastern United States of America (USA), Western Europe (WE), Indo-Gangetic Plain (IGP), East China (EC), and areas in South Africa (SA) and Middle East (MDE) are the major NO 2 hotspots in the world, which are also dominated by big cities with high anthropogenic activities. A significant decline (about-0.1 x 10 15 molec./cm 2 /year) in NO2 is found in the hotspots of USA and WE, and in their cities (e.g. New York, Boston, Brimingham, Los Angeles, Brussel, Paris, Berlin and London), which can be attributed to the substantial decline in NO2 emissions from road transport owing to their strict vehicular norms. Conversely, positive trends in NO2 are found in MDE, SA and IGP, along with their cities (e.g. Delhi, Johannesburg, Kuwait and Tehran), at about 0.04 - 0.1 x 10 15 molec./cm 2 /year; demanding stringent vehicular norms to curb the air pollution there.