( Pollutants ( ( are ( classified ( as ( ( primary or ) secondary ) ) ) ) . ) )
(ROOT (S (NP (NNS Pollutants)) (VP (VBP are) (VP (VBN classified) (PP (IN as) (NP (JJ primary) (CC or) (JJ secondary))))) (. .)))
Pollutants are classified as primary or secondary.
(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))))) (. .)))