( ( ( Number Concentration ) ( of ( Ultrafine ( Ambient ( Acid Particles ) ) ) ) ) . )
(ROOT (NP (NP (NNP Number) (NNP Concentration)) (PP (IN of) (NP (NNP Ultrafine) (NNP Ambient) (NNP Acid) (NNPS Particles))) (. .)))
Number Concentration of Ultrafine Ambient Acid Particles.
(ROOT (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NP (NNS particles)) (PP (IN of) (NP (NP (DT a) (NN substance)) (PP (IN in) (NP (DT a) (VBN given) (NN volume)))))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT the) (NN concentration))))) (. .)))