The pan-India Lockdown of 2020 due to COVID-19 pandemic as a turning point in impacting the environment and generating new trends lends it to specific analysis. In this context, the urban scenarios are most widely discussed and the Indian metropolitan cities stand pertinent examination. While many studies exist on analyzing air quality and air quality parameters in distribution and varying trends, works on highlighting the nature of dominant pollutant in time and space is not observed. The current study is distinctive in method as it tends to observe the evolving nature and distribution of primary pollutant in the air of two coastal cities of Chennai and Mumbai for every day of the COVID-19 nationwide Lockdown period of 2020. A comparative analysis is further attempted by taking air quality data for the period of national Lockdown in the matrix of 92*7 plus 92*4 time periods for Mumbai and Chennai respectively. Results reveal that despite being coastal in location, both cities have a distinct nature and distribution of Prominent Pollutant during this period. An examination of such a kind is pertinent in outlining the nature of pollution and its geographical dimensions across an urban area. This can help in the observation and management of pollution problem in a practical dimension.