( ( These pollutants ) ( ( react ( with ( ( water vapor ) ( in ( the ( clouds ( and ( form acids ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NNS pollutants)) (VP (VBP react) (PP (IN with) (NP (NP (NN water) (NN vapor)) (PP (IN in) (NP (DT the) (NNS clouds) (CC and) (NN form) (NNS acids)))))) (. .)))
These pollutants react with water vapor in the clouds and form acids.
(ROOT (S (NP (NNP Water) (NN vapor)) (VP (MD must) (VP (VB lose) (NP (NN heat) (NN energy)) (SBAR (IN before) (S (NP (NNS clouds)) (VP (MD can) (VP (VB form))))))) (. .)))
Water vapor must lose heat energy before clouds can form.