Since 1996, the EPA’s regulations for non-road diesel engines emissions have been phased in through four progressively more stringent tiers. Different tiers went into effect at different dates for different engines, but since 2015, all new non-road diesel engines, including stationary engines, but comply with the EPA’s Tier IV (Final) standard.
Today’s Tier IV compliant diesel engines are far more complex, efficient, and expensive than their unregulated ancestors from the early 1990’s.
How does Tier 4 compare with the previous generation (Tier III)?
For Tier III, the standard focused on reducing NOx (nitrous oxides) and NMHC (all hydrocarbons except methane) emissions to levels on par with federal requirements for on-road diesel engines. Since these non-road emissions were unregulated prior to the Tier Emissions Standards, we have no basis for a hard comparison, but the EPA estimates that since 2010, Tier III has been reducing NOx emissions by about 1 million tons per year. This is the amount of NOx produced annually by about 35 million cars.
Conspicuously absent from Tier III was any limit on PM (particulate matter), although the Tier II limit still applied to Tier III motors.