( ( Under ( most conditions ) ) ( , ( ( the ( air temperature ) ) ( ( decreases ( as ( altitude increases ) ) ) . ) ) ) )
(ROOT (S (PP (IN Under) (NP (JJS most) (NNS conditions))) (, ,) (NP (DT the) (NN air) (NN temperature)) (VP (VBZ decreases) (PP (IN as) (NP (NN altitude) (NNS increases)))) (. .)))
Under most conditions, the air temperature decreases as altitude increases.
(ROOT (S (NP (NNP Air) (NN temperature)) (VP (VBZ changes) (PP (IN as) (NP (NN altitude) (NNS increases)))) (. .)))