15A NCAC 02D .0404 CARBON MONOXIDE (a) The ambient air quality standards for carbon monoxide are: (1) (2) 9 parts per million (10 milligrams per cubic meter) maximum eight-hour average concentration not to be exceeded more than once per year, 35 parts per million (40 milligrams per cubic meter) maximum one-hour average concentration not to be exceeded more than once per year. (b) Sampling and analysis shall be in accordance with procedures in Appendix C 40 CFR Part 50 or equivalent methods established under 40 CFR Part 53. (c) An eight-hour average shall be considered valid if at least 75 percent of the hourly averages for the eight-hour period are available. In the event that only six or seven hourly averages are available, the eight-hour average shall be computed on the basis of the hours available using six or seven as the divisor. (d) When summarizing data for comparison with the standards, averages shall be stated to one decimal place. Comparison of the data with the levels of the standards in parts per million shall be made in terms of integers with fractional parts of 0.5 or greater rounding up. History Note: Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3); Eff. February 1, 1976; Amended Eff. October 1, 1989; July 1, 1984; December 1, 1976.