( ( ( ( Hydrocarbons ( -LRB- ( ( ( ( ( volatile ( organic compounds ) ) , ) or ) ( VOC 's ) ) -RRB- ) ) ) and ) ( ( ( ( ( nitrogen oxides ) ( -LRB- ( ( NO x ) -RRB- ) ) ) , ) ( the ( ozone precursors ) ) ) , ) ) ( chemically ( ( ( react ( in sunlight ) ) ( to ( form ozone ) ) ) . ) ) )
(ROOT (S (NP (NP (NP (NNS Hydrocarbons)) (PRN (-LRB- -LRB-) (NP (NP (JJ volatile)) (NP (JJ organic) (NNS compounds)) (, ,) (CC or) (NP (NNP VOC) (NNP 's))) (-RRB- -RRB-))) (CC and) (NP (NP (NP (NN nitrogen) (NNS oxides)) (PRN (-LRB- -LRB-) (INTJ (UH NO) (UH x)) (-RRB- -RRB-))) (, ,) (NP (DT the) (NN ozone) (NNS precursors)) (, ,))) (ADVP (RB chemically)) (VP (VBP react) (PP (IN in) (NP (NN sunlight))) (S (VP (TO to) (VP (VB form) (NP (NN ozone)))))) (. .)))
Hydrocarbons (volatile organic compounds, or VOC's) and nitrogen oxides (NO x ), the ozone precursors , chemically react in sunlight to form ozone.
(ROOT (S (NP (NN Ozone)) (VP (VBZ is) (NP (NP (DT a) (NN compound)) (VP (VBN formed) (SBAR (WHADVP (WRB when)) (S (NP (EX there)) (VP (VBZ is) (VP (VBG sparking) (NP (JJ electrical) (NN equipment))))))))) (. .)))