( ( CLASSIFY AIR ) ( ( POLLUTANTS 2 ) . ) )
(ROOT (S (NP (NNP CLASSIFY) (NNP AIR)) (VP (VBZ POLLUTANTS) (NP (CD 2))) (. .)))
CLASSIFY AIR POLLUTANTS 2.
(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))))) (. .)))