Dilution air background correction.

(a) Correct the emissions in a gaseous sample for background using the following equation: Where: x [emission]dexh = measured emission concentration in dilute exhaust (after dry-to-wet correction, if applicable). x [emission]bkgnd = measured emission concentration in the dilution air (after dry-to-wet correction, if applicable). DF = dilution factor, as determined in paragraph (b) of this section. Where: x CO2 = amount of CO 2 measured in the sample over the test interval. x NMHC = amount of C 1 -equivalent NMHC measured in the sample over the test interval. x CH4 = amount of CH 4 measured in the sample over the test interval. x CO = amount of CO measured in the sample over the test interval. a = atomic hydrogen-to-carbon ratio of the test fuel. You may measure a or use default values from Table 1 of 40 CFR 1065.655. b = atomic oxygen-to-carbon ratio of the test fuel. You may measure b or use default values from Table 1 of 40 CFR 1065.655. (c) Determine the dilution factor, DF , over the test interval for partial-flow dilution sample systems using the following equation: Where: V dexhstd = total dilute exhaust volume sampled over the test interval, corrected to standard reference conditions. V exhstd = total exhaust volume sampled from the vehicle, corrected to standard reference conditions. (d) Determine the time-weighted dilution factor, DF w , over the duty cycle using the following equation: Where: N = number of test intervals i = test interval number t = duration of the test interval DF = dilution factor over the test interval Example: N = 3 DF 1 = 14.40 t 1 = 505 s DF 2 = 24.48 t 2 = 867 s DF 3 = 17.28 t 3 = 505 s [79 FR 23823, Apr. 28, 2014, as amended at 86 FR 34583, June 29, 2021]