The fourth level of cell organization is the
tissue level
system level
organ level
organism level

The fourth level of cell organization is the organ system.  

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.