Who makes aftertreatment for AI data centers

Backup generators are permitted machines, and aftertreatment is what makes the permit achievable. Selective catalytic reduction injects urea to convert nitrogen oxides, diesel particulate filters trap soot, and oxidation catalysts handle carbon monoxide and hydrocarbons. Which of these is fitted depends entirely on the emissions tier the site is permitted to, and that depends on where it is and how many hours the engines may run. The permitting dimension is the whole story here. An engine used strictly for emergency backup faces one set of requirements; the same engine allowed to run for grid support, peak shaving or demand response faces a much stricter one, because the regulator is now treating it as a source of routine emissions rather than a rare one. Sites in areas with poor air quality have had generator counts and run hours limited outright, which has become a real constraint on where large campuses can be built. That matters to AI because the value of using a generator fleet for anything beyond emergencies has risen — a campus able to drop off the grid at peak is easier to interconnect. What to look for is the emissions tier a fleet is certified to, the permitted run hours, and whether the aftertreatment was specified for emergency duty only, because upgrading it later to unlock grid participation is a substantial retrofit.