Download the Code of Federal Regulations in XML.
The Electronic Code of Federal Regulations (e-CFR) is a regularly updated, unofficial editorial compilation of CFR material and Federal Register amendments produced by the National Archives and Records Administration's Office of the Federal Register (OFR) and the Government Publishing Office.
Parallel Table of Authorities and Rules for the Code of Federal Regulations and the United States Code
Text | PDF
Find, review, and submit comments on Federal rules that are open for comment and published in the Federal Register using Regulations.gov.
Purchase individual CFR titles from the U.S. Government Online Bookstore.
Find issues of the CFR (including issues prior to 1996) at a local Federal depository library.
Electronic Code of Federal Regulations
Title 40: Protection of Environment
§50.17 National primary ambient air quality standards for sulfur oxides (sulfur dioxide).
(a) The level of the national primary 1-hour annual ambient air quality standard for oxides of sulfur is 75 parts per billion (ppb, which is 1 part in 1,000,000,000), measured in the ambient air as sulfur dioxide (SO2).
(b) The 1-hour primary standard is met at an ambient air quality monitoring site when the three-year average of the annual (99th percentile) of the daily maximum 1-hour average concentrations is less than or equal to 75 ppb, as determined in accordance with appendix T of this part.
(c) The level of the standard shall be measured by a reference method based on appendix A or A-1 of this part, or by a Federal Equivalent Method (FEM) designated in accordance with part 53 of this chapter.
[75 FR 35592, June 22, 2010]