---
kind: "section"
citation: "40 C.F.R. § 1065.660"
title: "40"
number: "1065.660"
heading: "THC, NMHC, NMNEHC, CH 4 , and C 2 H 6 determination."
url: "https://uscodex.org/cfr/40/1065.660"
---

# §1065.660. THC, NMHC, NMNEHC, CH 4 , and C 2 H 6 determination.

- (a) **THC determination and initial THC/CH—** 4 contamination 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](/cfr/40/1065.520.md) as follows:

  Example:

  - (2) For the NMHC determination described in [paragraph (b)](#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)](#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)](#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.
  - (5) You may calculate THC as the sum of NMHC and CH4 if you determine CH4 with an FTIR as described in [paragraph (d)(2)](#d-2) of this section and NMHC with an FTIR using the additive method from [paragraph (b)(4)](#b-4) of this section.
  - (6) You may calculate THC as the sum of NMNEHC, C2H6, and CH4 if you determine CH4 with an FTIR as described in [paragraph (d)(2)](#d-2) of this section, C2H6 with an FTIR as described in [paragraph (e)](#e) of this section, and NMNEHC with an FTIR using the additive method from [paragraph (c)(3)](#c-3) of this section.
- (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)](/cfr/40/1065.650.md?p=c-5).
  - (2) For an NMC, calculate xNMHC using the NMC's penetration fractions, response factors, and/or combined penetration fractions and response factors as described in [§ 1065.365](/cfr/40/1065.365.md), the THC FID's CH4 response factor, RFCH4[THC-FID], from [§ 1065.360](/cfr/40/1065.360.md), the initial THC contamination and dry-to-wet corrected THC concentration, xTHC[THC-FID]cor, as determined in [paragraph (a)](#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)](#a) of this section.
    - (i) Use the following equation for an NMC configured as described in [§ 1065.365(d)](/cfr/40/1065.365.md?p=d):

      Eq. 1065.660-2

      Example:

    - (ii) Use the following equation for penetration fractions determined using an NMC configuration as outlined in [§ 1065.365(e)](/cfr/40/1065.365.md?p=e):

      Example:

    - (iii) Use the following equation for an NMC configured as described in [§ 1065.365(f)](/cfr/40/1065.365.md?p=f):

      Example:

  - (3) For a GC-FID or FTIR, calculate xNMHC using the THC analyzer's CH4 response factor, RFCH4[THC-FID], from [§ 1065.360](/cfr/40/1065.360.md), and the initial THC contamination and dry-to-wet corrected THC concentration, xTHC[THC-FID]cor, as determined in [paragraph (a)](#a) of this section as follows:

    Example:

    xTHC[THC-FID]cor = 145.6 µmol/mol

    RFCH4[THC-FID] = 0.970

    xCH4 = 18.9 µmol/mol

    xNMHC = 145.6—0.970 · 18.9

    xNMHC = 127.3 µmol/mol

  - (4) For an FTIR, calculate xNMHC by summing the hydrocarbon species listed in [§ 1065.266(c)](/cfr/40/1065.266.md?p=c) as follows:

    Example:

- (c) **NMNEHC determination.** Use one of the following methods to determine NMNEHC concentration, xNMNEHC:
  - (1) **Calculate <I>x</I><I>NMNEHC</I> based on the test fuel's ethane content as follows—**
    - (i) If the content of your test fuel contains less than 0.010 mol/mol of ethane, you may omit the calculation of NMNEHC concentration and calculate the mass of NMNEHC as described in [§ 1065.650(c)(6)(i)](/cfr/40/1065.650.md?p=c-6-i).
    - (ii) If the content of your fuel test contains at least 0.010 mol/mol of C2H6, you may omit the calculation of NMNEHC concentration and calculate the mass of NMNEHC as described in [§ 1065.650(c)(6)(ii)](/cfr/40/1065.650.md?p=c-6-ii).
  - (2) For a GC-FID, NMC FID, or FTIR, calculate xNMNEHC using the THC analyzer's CH4 response factor, RFCH4[THC-FID], and C2H6 response factor, RFC2H6[THC-FID], from [§ 1065.360](/cfr/40/1065.360.md), the initial contamination and dry-to-wet corrected THC concentration, xTHC[THC-FID]cor, as determined in [paragraph (a)](#a) of this section, the dry-to-wet corrected CH4 concentration, xCH4, as determined in [paragraph (d)](#d) of this section, and the dry-to-wet corrected C2H6 concentration, xC2H6, as determined in [paragraph (e)](#e) of this section as follows:

    Example:

  - (3) For an FTIR, calculate xNMNEHC by summing the hydrocarbon species listed in [§ 1065.266(c)](/cfr/40/1065.266.md?p=c) as follows:

    Example:

- (d) **CH—** 4 determination. Use one of the following methods to determine methane (CH4) concentration, xCH4:
  - (1) For an NMC, calculate xCH4 using the NMC's penetration fractions, response factors, and/or combined penetration fractions and response factors as described in [§ 1065.365](/cfr/40/1065.365.md), the THC FID's CH4 response factor, RFCH4[THC-FID], from [§ 1065.360](/cfr/40/1065.360.md), the initial THC contamination and dry-to-wet corrected THC concentration, xTHC[THC-FID]cor, as determined in [paragraph (a)](#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)](#a) of this section.
    - (i) Use the following equation for an NMC configured as described in [§ 1065.365(d)](/cfr/40/1065.365.md?p=d):

      Example:

    - (ii) Use the following equation for an NMC configured as described in [§ 1065.365(e)](/cfr/40/1065.365.md?p=e):

      Example:

    - (iii) Use the following equation for an NMC configured as described in [§ 1065.365(f)](/cfr/40/1065.365.md?p=f):

      Example:

  - (2) For a GC-FID or FTIR, xCH4 is the actual dry-to-wet corrected CH4 concentration as measured by the analyzer.
- (e) **C—** 2H6 determination. For a GC-FID or FTIR, xC2H6 is the C1-equivalent, dry-to-wet corrected C2H6 concentration as measured by the analyzer.

## Notes

### Amendments

[89 FR 29819, Apr. 22, 2024]

### Authority

Authority: 42 U.S.C. 7401-7671q.

### Source

Source: 70 FR 40516, July 13, 2005, unless otherwise noted.

### Amendments

[89 FR 29819, Apr. 22, 2024]