The rio grande river serves as a physical divider between mexico and canada

Ok that is not true at all it serves as a physical border between Mexico and the United States

Serves as a physical divider between Mexico and The United States

Air pollution: “combustion results in gases such as nitrogen oxides, nitrogen dioxide and particulates. the main causes of air pollution include transport, domestic combustion and industrial processes. pollutants from these sources can cause problems in the immediate vicinity and a distance away.”

81 is a composite number