{"data":{"id":"us/40-cfr-51.151","jurisdiction":"us","citation":"40 CFR 51.151","heading":"Significant harm levels.","body":"Each plan for a Priority I region must include a contingency plan which must, as a minimum, provide for taking action necessary to prevent ambient pollutant concentrations at any location in such region from reaching the following levels:\nSulfur dioxide—2.620 µg/m 3 (1.0 ppm) 24-hour average.\nPM10—600 micrograms/cubic meter; 24-hour average.\nCarbon monoxide—57.5 mg/m 3 (50 ppm) 8-hour average; 86.3 mg/m 3 (75 ppm) 4-hour average; 144 mg/m 3 (125 ppm) 1-hour average.\nOzone—1,200 ug/m 3 (0.6 ppm) 2-hour average.\nNitrogen dioxide—3.750 ug/m 3 (2.0 ppm) 1-hour average; 938 ug/m 3 (0.5 ppm) 24-hour average.","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER C—AIR PROGRAMS","PART 51—REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS","Subpart H—Prevention of Air Pollution Emergency Episodes"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"f8d431b18c59bd9148bac31e67e4a300c33ab14003a4d86bcf2acc224819e601","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-51.150","next":"us/40-cfr-51.152"},"notice":"GroundRules: Original legal text. Not legal advice."}