( ( ( Pollutant ( Primary Sources ) ) ( in ( the ( Air 1 ) ) ) ) . )
(ROOT (S (VP (VB Pollutant) (NP (JJ Primary) (NNS Sources)) (PP (IN in) (NP (DT the) (NNP Air) (CD 1)))) (. .)))
Pollutant Primary Sources in the Air 1.
(ROOT (S (NP (NP (NNP Ash)) (SBAR (WHNP (WDT that)) (S (VP (VBZ enters) (NP (DT the) (NN air)) (PP (ADVP (RB naturally)) (IN as) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (DT a) (NN volcano) (NN eruption))))))))) (VP (VBZ is) (VP (VBN classified) (PP (IN as) (NP (DT a) (JJ primary) (NN pollutant))))) (. .)))