We have been reading reports of animals venturing out into the cities, water in the rivers getting clearer and air quality becoming better, while humans are under lockdown.
Recently, data revealed by NASA showed that the metropolitan areas of the Northeast United States have seen significant reduction in air pollution.
Before:

After:

According to NASA, March 2020 recorded the lowest monthly atmospheric nitrogen dioxide levels during the month of March, since 2005. In fact, the levels of nitrogen dioxide in March, this year were about 30% lower than the average of the region spanning from Washington, DC to Boston.
Levels of nitrogen dioxide are used as an indicator to denote changes in human activity as it is emitted primarily from burning fossil fuels for transportation and electricity generation.

Similar such reductions in air pollution have also been observed in other parts of the world, including China and Italy.