( ( Toxic ( air pollutants ) ) ( ( are ( emitted ( ( ( by ( ( natural events ) ( -LRB- ( ( ( ( forest fires ) , ) volcanoes ) -RRB- ) ) ) ) ( as ( well as ) ) ) ( from ( industrial ( and ( mobile sources ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Toxic) (NN air) (NNS pollutants)) (VP (VBP are) (VP (VBN emitted) (PP (PP (IN by) (NP (NP (JJ natural) (NNS events)) (PRN (-LRB- -LRB-) (NP (NP (NN forest) (NNS fires)) (, ,) (NP (NNS volcanoes))) (-RRB- -RRB-)))) (CONJP (RB as) (RB well) (IN as)) (PP (IN from) (NP (JJ industrial) (CC and) (JJ mobile) (NNS sources)))))) (. .)))
Toxic air pollutants are emitted by natural events (forest fires, volcanoes) as well as from industrial and mobile sources.
(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))))) (. .)))