( ( Primary pollutants ) ( ( ( are usually ) ( produced ( from ( ( ( a process ) , ) ( such ( as ( ash ( from ( a ( volcanic eruption ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP are) (ADVP (RB usually)) (VP (VBN produced) (PP (IN from) (NP (NP (DT a) (NN process)) (, ,) (PP (JJ such) (IN as) (S (VP (VBG ash) (PP (IN from) (NP (DT a) (JJ volcanic) (NN eruption)))))))))) (. .)))
Primary pollutants are usually produced from a process, such as ash from a volcanic eruption.
(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))))) (. .)))