Table 2: National ambient air quility standards (NAAQS) for criteria air pollutants [59].

Criteria air pollutantPrimary standardSecondary standard
LevelAveraging TimeLevelAveraging Time

(1) Ozone0.075 ppm (2008 std)8 hoursSame as primary
(2) Particulate MatterSame as primary
 PM2.515.0 μg/m3 Annual
35 μg/m324 hoursSame as primary
 PM10150 μg/m3 24 hours
(3) Carbon Monoxide9 ppm (10 mg/m3)8 hoursNone
35 ppm (40 mg/m3)1 hour
(4) Nitrogen Dioxide*53 ppbAnnualSame as primary
100 ppb1 hourNone
(5) Sulfur Dioxide75 ppb1 hour0.5 ppm3 hour
(6) Lead0.15 μg/m3Rolling 3 month averageSame as primary

*Although NAAQS cover the entire group of NOX, NO2 is use as indicator for this group.