40 CFR 50.5 - National secondary ambient air quality standard for sulfur oxides (sulfur dioxide).

§ 50.5 National secondary ambient air quality standard for sulfur oxides (sulfur dioxide).
(a) The level of the 3-hour standard is 0.5 parts per million (ppm), not to be exceeded more than once per calendar year. The 3-hour averages shall be determined from successive nonoverlapping 3-hour blocks starting at midnight each calendar day and shall be rounded to 1 decimal place (fractional parts equal to or greater than 0.05 ppm shall be rounded up).
(b) Sulfur oxides shall be measured in the ambient air as sulfur dioxide by the reference method described in appendix A of this part or by an equivalent method designated in accordance with part 53 of this chapter.
(c) To demonstrate attainment, the second-highest 3-hour average must be based upon hourly data that are at least 75 percent complete in each calendar quarter. A 3-hour block average shall be considered valid only if all three hourly averages for the 3-hour period are available. If only one or two hourly averages are available, but the 3-hour average would exceed the level of the standard when zeros are substituted for the missing values, subject to the rounding rule of paragraph (a) of this section, then this shall be considered a valid 3-hour average. In all cases, the 3-hour block average shall be computed as the sum of the hourly averages divided by 3.
[61 FR 25580, May 22, 1996]

Title 40 published on 2014-07-01

no entries appear in the Federal Register after this date.

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United States Code

Title 40 published on 2014-07-01

The following are ALL rules, proposed rules, and notices (chronologically) published in the Federal Register relating to 40 CFR 50 after this date.

  • 2014-12-17; vol. 79 # 242 - Wednesday, December 17, 2014
    1. 79 FR 75234 - National Ambient Air Quality Standards for Ozone
      GPO FDSys XML | Text
      Proposed rule.
      Written comments on this proposed rule must be received by March 17, 2015. Public Hearings: The EPA intends to hold three public hearings on this proposed rule in January 2015. These will be announced in a separate Federal Register notice that provides details, including specific dates, times, addresses, and contact information for these hearings.
      40 CFR Parts 50, 51, 52, 53, and 58