( ( These pollutants ) ( ( ( are all ) ( ( called ( primary pollutants ) ) ( because ( they ( have ( direct sources ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NNS pollutants)) (VP (VBP are) (RB all) (VP (VBN called) (NP (JJ primary) (NNS pollutants)) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP have) (NP (JJ direct) (NNS sources))))))) (. .)))
These pollutants are all called primary pollutants because they have direct sources.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))