( ( When ( humans ( burn ( fossil fuels ) ) ) ) ( , ( ( ( ( ( sulfur dioxide ) ( -LRB- ( SO2 -RRB- ) ) ) and ) ( ( nitrogen oxides ) ( -LRB- ( NOx -RRB- ) ) ) ) ( ( are ( released ( into ( the atmosphere ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NNS humans)) (VP (VBP burn) (NP (JJ fossil) (NNS fuels))))) (, ,) (NP (NP (NP (NN sulfur) (NN dioxide)) (PRN (-LRB- -LRB-) (NP (NNP SO2)) (-RRB- -RRB-))) (CC and) (NP (NP (NN nitrogen) (NNS oxides)) (PRN (-LRB- -LRB-) (NP (NNP NOx)) (-RRB- -RRB-)))) (VP (VBP are) (VP (VBN released) (PP (IN into) (NP (DT the) (NN atmosphere))))) (. .)))
When humans burn fossil fuels, sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere.
(ROOT (S (NP (DT The) (NN element) (NN sulfur)) (VP (VBZ is) (VP (VBN released) (PP (IN into) (NP (DT the) (NN atmosphere))) (PP (IN by) (NP (NP (DT the) (NN burning)) (PP (IN of) (NP (JJ fossil) (NNS fuels))))))) (. .)))