( ( ( ( ( Volatile ( organic ( compounds ( and ( nitrogen oxides ) ) ) ) ) , ) ( the ( ozone precursors ) ) ) , ) ( chemically ( ( react ( in ( ( ( ( sunlight ( to ( form ( ground ( level ozone ) ) ) ) ) , ) or ) smog ) ) ) . ) ) )
(ROOT (S (NP (NP (JJ Volatile) (JJ organic) (NNS compounds) (CC and) (NN nitrogen) (NNS oxides)) (, ,) (NP (DT the) (NN ozone) (NNS precursors)) (, ,)) (ADVP (RB chemically)) (VP (VBP react) (PP (IN in) (S (VP (VP (VBG sunlight) (S (VP (TO to) (VP (VB form) (NP (NN ground) (NN level) (NN ozone)))))) (, ,) (CC or) (VP (VBG smog)))))) (. .)))
Volatile organic compounds and nitrogen oxides, the ozone precursors, chemically react in sunlight to form ground level ozone, or smog.
(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))))))))) (. .)))