( ( The Board ) ( ( has ( ( treated ( ( a variety ) ( of ( ( substances or ) elements ) ) ) ) ( as ( air pollution ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNP Board)) (VP (VBZ has) (VP (VBN treated) (NP (NP (DT a) (NN variety)) (PP (IN of) (NP (NNS substances) (CC or) (NNS elements)))) (PP (IN as) (NP (NN air) (NN pollution))))) (. .)))
The Board has treated a variety of substances or elements as air pollution.
(ROOT (S (NP (NNP Air)) (VP (MD can) (VP (VB be) (VP (VBN separated) (PP (IN into) (NP (JJ several) (NNS elements)))))) (. .)))