# How do coal rollers control when their vehicle spews black smoke and when it does not? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2021, 10:09pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512 "2021-07-14T22:09:37Z")\ **Posts on this page:** 1\ **Showing post:** 11
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 19, 2021, 5:01pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/11 "2021-07-19T17:01:31Z")
States don’t usually check individual vehicle emissions unless they have a problem meeting NAAQS: > **[National Ambient Air Quality Standards](https://en.wikipedia.org/wiki/National_Ambient_Air_Quality_Standards)** > > The U.S. National Ambient Air Quality Standards (NAAQS, pronounced /ˈnæks/ naks) are limits on atmospheric concentration of six pollutants that cause smog, acid rain, and other health hazards. Established by the United States Environmental Protection Agency (EPA) under authority of the Clean Air Act (42 U.S.C. 7401 et seq.), NAAQS is applied for outdoor air throughout the country. > The six criteria air pollutants (CAP), or criteria pollutants, for which limits are set in the NAAQS are ozone (O3),... If a state or region is found to be in violation of EPA-mandated NAAQS, then they’re required to develop a SIP: > **[Basic Information about Air Quality SIPs | US EPA](https://www.epa.gov/air-quality-implementation-plans/basic-information-about-air-quality-sips)** > > This page provides basic information on a State Implementation Plan. A SIP is a state’s plan for achieving NAAQS compliance and often targets privately owned vehicles, either with an annual smog check requirement, or (as Denver does) a drive-by roadside emissions check. > [@How does this drive-by emissions test work? (Northern Virginia)](https://boards.straightdope.com/t/how-does-this-drive-by-emissions-test-work-northern-virginia/845513/15): > > The typical location is a highway on-ramp where you are accelerating, i.e. you’re making a significant amount of power (and therefore a useful amount of exhaust). The measurement is optical: the system is sending a light beam across the roadway, roughly through the region where your car will be spewing exhaust, and a receiver on the far side of the road measures the attenuation of specific wavelengths of the beam by the components of your exhaust. The higher the concentration of criteria pol… If a state is in NAAQS compliance, then they often aren’t equipped to do emissions checks. As noted upthread though, the EPA is targeting bigger fish, with some success: > **[EPA says Windham dealership tampered with truck emissions controls](https://www.pressherald.com/2021/07/16/epa-says-windham-dealership-tampered-with-truck-emissions-controls/)** > > The federal agency is seeking a $168,700 fine for the alleged violations of the Clean Air Act. > **[Clean Air Act Vehicle and Engine Enforcement Case Resolutions | US EPA](https://www.epa.gov/enforcement/clean-air-act-vehicle-and-engine-enforcement-case-resolutions)** > > The Clean Air Act requires new engines and equipment sold or distributed in the United States to be certified to meet EPA-established emissions requirements to protect public health and the environment from air pollution. --- _[View the full topic](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512)._