▁in ▁between ▁ 1 9 9 8 ▁and ▁ 2 0 0 6 , ▁are ▁considered ▁aver aging ▁standards , ▁because ▁they ▁allow ▁manufact ur ers ▁to ▁offset ▁more - p oll uting ▁engines ▁in ▁their ▁product ▁range ▁by ▁offering ▁other ▁engines ▁that ▁exceed ▁the ▁standard . ▁California ▁and ▁subsequently ▁New ▁York ▁have , ▁in ▁turn , ▁adopted ▁more ▁string ent ▁reg ulations ▁than ▁the ▁federal ▁standard . ▁Sub sequ ent ▁to ▁ 2 0 0 4 ▁when ▁the ▁maximum ▁emission ▁redu ctions ▁required ▁by ▁California ▁became ▁effective , ▁the ▁substantial ▁majority ▁of ▁new ▁P W C ▁units ▁sold ▁throughout ▁the ▁United ▁States ▁have ▁met ▁the ▁lower ▁em issions ▁standards ▁established ▁by ▁California . ▁ ▁To ▁meet ▁these ▁reg ulations , ▁manufact ur ers ▁have ▁adopted ▁a ▁variety ▁of ▁improvements , ▁including ▁increased ▁use ▁of ▁four - stroke ▁engines , ▁the ▁use ▁of ▁direct ▁injection ▁for ▁two - st ro kes , ▁and ▁the ▁use ▁of ▁catal yt ic ▁conver ters ▁and ▁other ▁poll ution - cur bing ▁measures ▁that ▁overall ▁have ▁reduced ▁em issions ▁by ▁approximately ▁ 7 5 % ▁compared ▁to ▁pre - reg ulation ▁models . ▁ ▁In ▁some ▁areas , ▁such ▁as ▁Lake ▁T ah oe , ▁out board ▁mot ors ▁and ▁P W C s ▁are ▁permitted ▁if ▁they ▁meet ▁the ▁ 2 0 0 6 ▁E PA ▁or ▁California ▁Air ▁Resources ▁Board ▁( C AR B ) ▁ 2 0 0 1 ▁reg ulations . ▁Some ▁pre - 2 0 0 6 ▁model ▁year ▁P W C