( Concentration ( ( means ( ( a measure ) ( of ( ( the amount ) ( of ( ( a substance ) ( contained ( per ( ( unit volume ) ( of air ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Concentration)) (VP (VBZ means) (NP (NP (DT a) (NN measure)) (PP (IN of) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (DT a) (NN substance)) (VP (VBN contained) (PP (IN per) (NP (NP (NN unit) (NN volume)) (PP (IN of) (NP (NN air)))))))))))) (. .)))
Concentration means a measure of the amount of a substance contained per unit volume of air.
(ROOT (S (NP (NN Volume)) (VP (VBZ is) (NP (NP (DT a) (NN measure)) (PP (IN of) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NN space)))))) (SBAR (IN that) (S (NP (NP (DT a) (NN substance)) (CC or) (NP (DT an) (NN object))) (VP (VBZ occupies))))) (. .)))