{"data":{"id":"us/40-cfr-1065.659","jurisdiction":"us","citation":"40 CFR 1065.659","heading":"Removed water correction.","body":"(a) If you remove water upstream of a concentration measurement, x, correct for the removed water. Perform this correction based on the amount of water at the concentration measurement, xH2O[emission]meas, and at the flow meter, xH2Oexh, whose flow is used to determine the mass emission rate or total mass over a test interval. For continuous analyzers downstream of a sample dryer for transient and ramped-modal cycles, you must apply this correction on a continuous basis over the test interval, even if you use one of the options in § 1065.145(e)(2) that results in a constant value for xH2O[emission]meas because xH2Oexh varies over the test interval. For batch analyzers, determine the flow-weighted average based on the continuous xH2Oexh values determined as described in paragraph (c) of this section. For batch analyzers, you may determine the flow-weighted average xH2Oexh based on a single value of xH2Oexh determined as described in paragraphs (c)(2) and (3) of this section, using flow-weighted average or batch concentration inputs.\n(b) Determine the amount of water remaining downstream of a sample dryer and at the concentration measurement using one of the methods described in § 1065.145(e)(2). If you use a sample dryer upstream of an analyzer and if the calculated amount of water remaining downstream of the sample dryer and at the concentration measurement, xH2O[emission]meas, is higher than the amount of water at the flow meter, xH2Oexh, set xH2O[emission]meas equal to xH2Oexh. If you use a sample dryer upstream of storage media, you must be able to demonstrate that the sample dryer is removing water continuously (i.e., xH2Oexh is higher than xH2O[emission]meas throughout the test interval).\n(c) For a concentration measurement where you did not remove water, you may set xH2O[emission]meas equal to xH2Oexh. You may determine the amount of water at the flow meter, xH2Oexh, using any of the following methods:\n(1) Measure the dewpoint and absolute pressure and calculate the amount of water as described in § 1065.645.\n(2) If the measurement comes from raw exhaust, you may determine the amount of water based on intake-air humidity, plus a chemical balance of fuel, DEF, intake air, and exhaust as described in § 1065.655.\n(3) If the measurement comes from diluted exhaust, you may determine the amount of water based on intake-air humidity, dilution air humidity, and a chemical balance of fuel, DEF, intake air, and exhaust as described in § 1065.655.\n(d) Perform a removed water correction to the concentration measurement using the following equation:","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1065—ENGINE-TESTING PROCEDURES","Subpart G—Calculations and Data Requirements"],"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":"d7b909fb2694e1a130e9128b629173337d05fd52fcda0ca0d0981ea9b5ae41ad","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1065.656","next":"us/40-cfr-1065.660"},"notice":"GroundRules: Original legal text. Not legal advice."}