StacksVerified U.S. regulatory reference

40 CFR §1039.105

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
  1. (a)The smoke opacity standards in this section apply to all engines subject to emission standards under this part, except for the following engines:
    1. (1)Single-cylinder engines.
    2. (2)Constant-speed engines.
    3. (3)Engines certified to a PM emission standard or FEL of 0.07 g/kW-hr or lower.
  2. (b)Measure smoke opacity as specified in § 1039.501(c). Smoke opacity from your engines may not exceed the following standards:
    1. (1)20 percent during the acceleration mode.
    2. (2)15 percent during the lugging mode.
    3. (3)50 percent during the peaks in either the acceleration or lugging modes.