Decomposers serve a key role in the nitrogen cycle, primarily because they

Break down dead material and release the nitrogen from the dead material back into the nitrogen cycle. The nitrogen would be trapped without the decomposers.

Explanation:

significant amounts of nitrogen oxides, carbon monoxide, and other pollution

explanation:

passenger vehicles are a major pollution contributor, producing significant amounts of nitrogen oxides, carbon monoxide, and other pollution. in 2013, transportation contributed more than half of the carbon monoxide and nitrogen oxides, and almost a quarter of the hydrocarbons emitted into our air.