( ( In ( ( the presence ) ( of sunlight ) ) ) ( , ( ( these compounds ) ( ( form ( ( ( ground-level ozone ) , ) ( ( the ( primary component ) ) ( of smog ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (NN presence)) (PP (IN of) (NP (NN sunlight))))) (, ,) (NP (DT these) (NNS compounds)) (VP (VBP form) (NP (NP (JJ ground-level) (NN ozone)) (, ,) (NP (NP (DT the) (JJ primary) (NN component)) (PP (IN of) (NP (NN smog)))))) (. .)))
In the presence of sunlight, these compounds form ground-level ozone, the primary component of 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))))))))) (. .)))