Anticipating the novel coronavirus disease (COVID-19) pandemic

Taranjot Kaur; Sukanta Sarkar; Sourangsu Chowdhury; Sudipta Kumar Sinha; Mohit Kumar Jolly; Partha Sharathi Dutta

The rigor of social distancing/intervention strategies can be measured by atmospheric data, as the lockdown periods have witnessed better air quality across the globe. Thus, we first obtain time-series of triads of the population-weighted total-column NO 2 (molecules/cm 2 ) density over the length of the study period for the nine countries considered in this work (the circular points in Fig. 6 ). The solid curve in each subfigure of Fig. 6 represents a 10-triad moving window average. In the majority of the countries, the timing of NO 2 decline concurs with the spread of the virus and the onset of pragmatic lockdown in a country may be hypothesized by the reversal (or break) in the trend of NO 2 . In China (Fig 6B) , the decreasing trend in NO 2 is evident from January end till February; after that, it starts increasing which is coincident with the dynamics of the spread of COVID-19 disease. In India (Fig 6A) , South Korea (Fig 6C) , US (Fig 6D) , Italy ( Fig 6G) and Spain (Fig 6F) , the decreasing trend in NO 2 coincides with time of the rapid spread in the virus (Fig. 1) . We estimate that after the date of official enforcement of lockdown, time-averaged NO 2 decreased by 35.9% in China and 50.4% in Italy compared to the pre-lockdown period. India has also seen a significant drop by 5% of NO 2 in the last 2 triads around the day of "Janata curfew". The decreased pattern in NO 2 is expected to continue as the lockdown prevails up to 14 April. It should be noted that we did not control for meteorological variations which may have a significant impact on total-column NO 2 over the period of our study [27] . Overall, amidst the fears of the novel coronavirus, the countries where the lockdown intervened are expecting a rejuvenated environment. However, at the same time, possibilities to lower down air pollutants when the world is not facing such harsh conditions is also important to understand.