Code of Federal Regulations Title 40. Protection of Environment § 40.50.16 National primary and secondary ambient air quality standards for lead

(a) The national primary and secondary ambient air quality standards for lead (Pb) and its compounds are 0.15 micrograms per cubic meter, arithmetic mean concentration over a 3–month period, measured in the ambient air as Pb either by:

(b) The national primary and secondary ambient air quality standards for Pb are met when the maximum arithmetic 3–month mean concentration for a 3–year period, as determined in accordance with appendix R of this part, is less than or equal to 0.15 micrograms per cubic meter.