Why Do Cities in Warm and Dry Climates Tend to Have

Why do cities in warm and dry climates tend to have more air pollution?

A) There are more automobiles in these areas.
B) These locations are usually surrounded by mountains that trap the air pollution.
C) There are more plants and trees that promote the formation of VOCs.
D) There are more chemical reactions that can happen in dry climates.
E) There are fewer natural pollution reduction factors such as precipitation and salty sea spray.