(a) Correct the emissions in a gaseous sample for background using the following equation:

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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:xCO2 = amount of CO2 measured in the sample over the test interval.xNMHC = amount of C1-equivalent NMHC measured in the sample over the test interval.xCH4 = amount of CH4 measured in the sample over the test interval.xCO = 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:

Vdexhstd = total dilute exhaust volume sampled over the test interval, corrected to standard reference conditions.

Vexhstd = total exhaust volume sampled from the vehicle, corrected to standard reference conditions.

(d) Determine the time-weighted dilution factor, DFw, over the duty cycle using the following equation:

Where:N = number of test intervalsi = test interval numbert = duration of the test intervalDF = dilution factor over the test intervalExample: N = 3DF1 = 14.40t1 = 505 sDF2 = 24.48t2 = 867 sDF3 = 17.28t3 = 505 s[79 FR 23823, Apr. 28, 2014, as amended at 86 FR 34583, June 29, 2021]