North American pollution controls take effect.
D000397:Air Pollution / Q000331:legislation & jurisprudence / Q000517:prevention & control*; D006076:Government; D006801:Humans; D007221:Industry; D007373:Interinstitutional Relations; D007391:International Cooperation; D009656:North America; D010083:Oxidants, Photochemical; D010126:Ozone; D011050:Policy Making; D011210:Power Plants; D011640:Public Policy; D012016:Reference Values
D010083:Oxidants, Photochemical; D010126:Ozone