( Today ( , ( ( motor vehicles ) ( ( are ( the ( primary ( air polluter ) ) ) ) . ) ) ) )
(ROOT (S (NP (NN Today)) (, ,) (NP (NN motor) (NNS vehicles)) (VP (VBP are) (NP (DT the) (JJ primary) (NN air) (NN polluter))) (. .)))
Today, motor vehicles are the primary air polluter.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))