The E.P.A has recently set a lower limit for the amount of soot particles in the air. The limit is now 12 µ gms per cubic meter, lowered from 15 µ gms previously . Indian air quality standards are much less strict.
http://www.nytimes.com/2012/12/15/science/earth/epa-proposes-tighter-soot-rule.html?emc=eta1&_r=0
indiaairquality 