( ( Hazardous ( air pollutants ) ) ( ( ( ( come ( ( ( from ( ( natural sources ) ( such ( as ( forest ( ( fires and ) volcanoes ) ) ) ) ) ) and ) ( from ( human sources ) ) ) ) , ) ( both ( ( stationary and ) mobile ) ) ) . ) )
(ROOT (S (NP (JJ Hazardous) (NN air) (NNS pollutants)) (VP (VBD come) (PP (PP (IN from) (NP (NP (JJ natural) (NNS sources)) (PP (JJ such) (IN as) (NP (NN forest) (NNS fires) (CC and) (NNS volcanoes))))) (CC and) (PP (IN from) (NP (JJ human) (NNS sources)))) (, ,) (ADJP (DT both) (JJ stationary) (CC and) (JJ mobile))) (. .)))
Hazardous air pollutants come from natural sources such as forest fires and volcanoes and from human sources, both stationary and mobile.
(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))))) (. .)))