Section 24-147. Emission of nitrogen oxides

No person shall cause or permit
  emission of an air contaminant:
    (a) from a boiler with a capacity of five hundred million Btu per hour
  or  more  and  completed  after  August  twentieth,   nineteen   hundred
  seventy-one,  if the air contaminant emitted has nitrogen oxides content
  of more than one hundred  parts  per  million  by  volume  of  undiluted
  emissions at ten percent excess air.
    (b) from a boiler with a capacity of five hundred million Btu per hour
  or   more  and  completed  before  August  twentieth,  nineteen  hundred
  seventy-one, if the air contaminant emitted has nitrogen oxides  content
  of  more than one hundred fifty parts per million by volume of undiluted
  emissions at ten percent excess air.