This step of the analysis employs complex computer models that simulate the transport and transformation of emitted pollutants in the atmosphere.
( ( ( This step ) ( of ( the analysis ) ) ) ( ( employs ( ( complex ( computer models ) ) ( that ( simulate ( ( the ( ( transport and ) transformation ) ) ( of ( ( emitted pollutants ) ( in ( the atmosphere ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT This) (NN step)) (PP (IN of) (NP (DT the) (NN analysis)))) (VP (VBZ employs) (NP (NP (JJ complex) (NN computer) (NNS models)) (SBAR (WHNP (WDT that)) (S (VP (VBP simulate) (NP (NP (DT the) (NX (NX (NN transport)) (CC and) (NX (NN transformation)))) (PP (IN of) (NP (NP (JJ emitted) (NNS pollutants)) (PP (IN in) (NP (DT the) (NN atmosphere))))))))))) (. .)))
This analysis uses complex computer models to simulate transport and transformation of pollutants 
( ( This analysis ) ( ( uses ( complex ( computer models ) ) ) ( to ( ( simulate ( ( transport and ) transformation ) ) ( of pollutants ) ) ) ) )
(ROOT (S (NP (DT This) (NN analysis)) (VP (VBZ uses) (NP (JJ complex) (NN computer) (NNS models)) (PP (TO to) (NP (NP (JJ simulate) (NX (NX (NN transport)) (CC and) (NX (NN transformation)))) (PP (IN of) (NP (NNS pollutants))))))))