What Affect has the global quarantine had On air quality world wide.?

In some areas, it has cleansed the atmosphere.

Explanation:

Since people are supposed to leave only out of necessity, they have been using their vehicles less, therefore, the pollution is decreasing.  

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.