( ( ( ( The decrease ) ( in ( air pressure ) ) ) ( as ( height increases ) ) ) . )
(ROOT (NP (NP (DT The) (NN decrease)) (PP (IN in) (NP (NN air) (NN pressure))) (PP (IN as) (NP (NN height) (NNS increases))) (. .)))
The decrease in air pressure as height increases.
(ROOT (S (NP (NNP Air)) (VP (VBP pressure) (SBAR (S (NP (PRP it)) (VP (VBZ decreases) (PP (IN as) (NP (NN altitude) (NNS increases))))))) (. .)))