( ( ( The ( primary contributor ) ) ( of ( ( air pollutants ) ( in ( the region ) ) ) ) ) ( ( is ( mobile emissions ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ primary) (NN contributor)) (PP (IN of) (NP (NP (NN air) (NNS pollutants)) (PP (IN in) (NP (DT the) (NN region)))))) (VP (VBZ is) (NP (JJ mobile) (NNS emissions))) (. .)))
The primary contributor of air pollutants in the region is mobile emissions.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))