No person shall cause or permit to be discharged into the outdoor atmosphere from any single source of emission whatsoever any visible air contaminant of a density darker than No. 1 on the Ringelmann Chart or greater than 20% opacity except:
(a) Any visible air contaminant of a density not darker than No. 2 on the Ringelmann Chart or greater than 40% opacity may be emitted for a period or periods aggregating not more than three minutes in any sixty minute period, but such emissions shall not be permitted on more than three occasions during any twenty-four hour period.
(b) Where the presence of uncombined water vapor is the only reason for failure of an emission to meet the requirements of this section.
(Ord. 2494, passed 5-12-1975)