( ( ( ( ( ( Light pollution ) , ) or ) ( ( extra light ) ( directed ( into ( ( the sky ) ( where ( it ( ( is not ) needed ) ) ) ) ) ) ) ) , ) ( ( is ( ( the ( primary cause ) ) ( of ( ( poor ( night viewing ) ) ( in ( ( ( cities , ) not ) ( the ( air pollution ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (JJ Light) (NN pollution)) (, ,) (CC or) (NP (NP (JJ extra) (NN light)) (VP (VBN directed) (PP (IN into) (NP (NP (DT the) (NN sky)) (SBAR (WHADVP (WRB where)) (S (NP (PRP it)) (VP (VBZ is) (RB not) (VP (VBN needed))))))))) (, ,)) (VP (VBZ is) (NP (NP (DT the) (JJ primary) (NN cause)) (PP (IN of) (NP (NP (JJ poor) (NN night) (VBG viewing)) (PP (IN in) (NP (NP (NNS cities)) (, ,) (RB not) (NP (DT the) (NN air) (NN pollution)))))))) (. .)))
Light pollution, or extra light directed into the sky where it is not needed, is the primary cause of poor night viewing in cities, not the air pollution.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))