---
kind: "section"
citation: "40 C.F.R. § 1065.1005"
title: "40"
number: "1065.1005"
heading: "Symbols, abbreviations, acronyms, and units of measure."
url: "https://uscodex.org/cfr/40/1065.1005"
---

# §1065.1005. Symbols, abbreviations, acronyms, and units of measure.


The procedures in this part generally follow the International System of Units (SI), as detailed in NIST Special Publication 811, which we incorporate by reference in [§ 1065.1010](/cfr/40/1065.1010.md). See [§ 1065.20](/cfr/40/1065.20.md) for specific provisions related to these conventions. This section summarizes the way we use symbols, units of measure, and other abbreviations.

- (a) **Symbols for quantities.** This part uses the following symbols and units of measure for various quantities:
- (b) **Symbols for chemical species.** This part uses the following symbols for chemical species and exhaust constituents:
- (c) **Prefixes.** This part uses the following prefixes for units and unit symbols:
- (d) **Superscripts—** . This part uses the following superscripts for modifying quantity symbols:
- (e) **Subscripts—** . This part uses the following subscripts for modifying quantity symbols:
- (f) **Constants.**
  - (1) **This part uses the following constants for the composition of dry air—**
  - (2) **This part uses the following molar masses or effective molar masses of chemical species—**
  - (3) **This part uses the following molar gas constant for ideal gases—**
  - (4) **This part uses the following ratios of specific heats for dilution air and diluted exhaust—**
- (g) **Other acronyms and abbreviations.** This part uses the following additional abbreviations and acronyms:

## Notes

### Amendments

[79 FR 23815, Apr. 28, 2014, as amended at 81 FR 74191, Oct. 25, 2016; 86 FR 34575, June 29, 2021; 87 FR 64866, Oct. 26, 2022; 88 FR 4689, Jan. 24, 2023]

### Authority

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

### Source

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

### Amendments

[79 FR 23815, Apr. 28, 2014, as amended at 81 FR 74191, Oct. 25, 2016; 86 FR 34575, June 29, 2021; 87 FR 64866, Oct. 26, 2022; 88 FR 4689, Jan. 24, 2023]