# 40 CFR § 1065.660 - THC, NMHC, NMNEHC, CH4, and C2H6 determination.

(a) THC determination and initial THC/CH4contamination corrections.

(1) If we require you to determine THC emissions, calculate xTHC[THC-FID]cor using the initial THC contamination concentration xTHC[THC-FID]init from § 1065.520 as follows:

(2) For the NMHC determination described in paragraph (b) of this section, correct xTHC[THC-FID] for initial THC contamination using Eq. 1065.660-1. You may correct xTHC[NMC-FID] for initial contamination of the CH4 sample train using Eq. 1065.660-1, substituting in CH4 concentrations for THC.

(3) For the NMNEHC determination described in paragraph (c) of this section, correct xTHC[THC-FID] for initial THC contamination using Eq. 1065.660-1. You may correct xTHC[NMC-FID] for initial contamination of the CH4 sample train using Eq. 1065.660-1, substituting in CH4 concentrations for THC.

(4) For the CH4 determination described in paragraph (d) of this section, you may correct xTHC[NMC-FID] for initial THC contamination of the CH4 sample train using Eq. 1065.660-1, substituting in CH4 concentrations for THC.

(b) NMHC determination. Use one of the following to determine NMHC concentration, xNMHC:

(1) If you do not measure CH4, you may omit the calculation of NMHC concentrations and calculate the mass of NMHC as described in § 1065.650(c)(5).

(2) For nonmethane cutters, calculate xNMHC using the nonmethane cutter's penetration fraction (PF) of CH4 and the response factor penetration fraction (RFPF) of C2H6 from § 1065.365, the response factor (RF) of the THC FID to CH4 from § 1065.360, the initial THC contamination and dry-to-wet corrected THC concentration xTHC[THC-FID]cor as determined in paragraph (a) of this section, and the dry-to-wet corrected CH4 concentration xTHC[NMC-FID]cor optionally corrected for initial THC contamination as determined in paragraph (a) of this section.

(i) Use the following equation for penetration fractions determined using an NMC configuration as outlined in § 1065.365(d):

(ii) For penetration fractions determined using an NMC configuration as outlined in section § 1065.365(e), use the following equation:

(iii) For penetration fractions determined using an NMC configuration as outlined in section § 1065.365(f), use the following equation:

(3) For a GC-FID or FTIR, calculate xNMHC using the THC analyzer's response factor (RF) for CH4, from § 1065.360, and the initial THC contamination and dry-to-wet corrected THC concentration xTHC[THC-FID]cor as determined in paragraph (a) of this section as follows:

(4) For an FTIR, calculate xNMHC by summing the hydrocarbon species listed in § 1065.266(c) as follows:

(c) NMNEHC determination. Use one of the following methods to determine NMNEHC concentration, xNMNEHC:

(1) If the content of your test fuel contains less than 0.010 mol/mol of ethane, you may omit the calculation of NMNEHC concentrations and calculate the mass of NMNEHC as described in § 1065.650(c)(6).

(2) For a GC-FID or FTIR, calculate xNMNEHC using the THC analyzer's response factors (RF) for CH4 and C2H6, from § 1065.360, and the initial contamination and dry-to-wet corrected THC concentration xTHC[THC-FID]cor as determined in paragraph (a) of this section as follows:

(3) For an FTIR, calculate xNMNEHC by summing the hydrocarbon species listed in § 1065.266(c) as follows:

(d) CH4determination. Use one of the following methods to determine CH4 concentration, xCH4:

(1) For nonmethane cutters, calculate xCH4 using the nonmethane cutter's penetration fraction (PF) of CH4 and the response factor penetration fraction (RFPF) of C2H6 from § 1065.365, the response factor (RF) of the THC FID to CH4 from § 1065.360, the initial THC contamination and dry-to-wet corrected THC concentration xTHC[THC-FID]cor as determined in paragraph (a) of this section, and the dry-to-wet corrected CH4 concentration xTHC[NMC-FID]cor optionally corrected for initial THC contamination as determined in paragraph (a) of this section.

(i) Use the following equation for penetration fractions determined using an NMC configuration as outlined in § 1065.365(d):

(ii) For penetration fractions determined using an NMC configuration as outlined in § 1065.365(e), use the following equation:

(iii) For penetration fractions determined using an NMC configuration as outlined in § 1065.365(f), use the following equation:

(2) For a GC-FID or FTIR, xCH4 is the actual dry-to-wet corrected CH4 concentration as measured by the analyzer.

(e) C2H6determination. For a GC-FID or FTIR, xC2H6 is the C1-equivalent, dry-to-wet corrected C2H6 concentration as measured by the analyzer.