Decline in PM_2.5 concentrations over major cities around the world associated with COVID-19

The COVID-19 started from Wuhan city in China, slowly spread across the globe after December 2019. Due to movement of people from one city to other cities, one country to other countries, infection spreads and COVID-19 became a pandemic. Efforts were made at local, regional and national levels to lockdown the movement of people and to keep infected one in quarantine or isolation to stop the spread of COVID-19. The traffic, market and small industries were closed, as a result pronounced decline in the concentrations of particulate matters (PM) were observed. Normally these sources contribute to the high concentrations of particulate matters (PM_2.5) which represents air quality of a location. In this short communication, we present analysis of PM_2.5 of major cities (New York, Los Angeles, Zaragoza, Rome, Dubai, Delhi, Mumbai, Beijing and Shanghai) around the world suffered severely with the COVID-19. Our analysis shows decline in PM_2.5 concentration due to lockdown, mainly due to less movement of people to keep "social distancing" to control the spread of CORONA-19. The low concentrations of PM_2.5 reflect the efforts made in the cities to curb the spread of infection, that improve air quality.