Missouri Engines Get Simpler NOX Reporting Rules
Published Date: 7/15/2026
Proposed Rule
Summary
The EPA wants to approve updates to Missouri’s rules for big stationary engines that release nitrogen oxides (NOX), a harmful air pollutant. These updates simplify reporting, add clear definitions, remove confusing rules, and exempt some spark-ignited engines. If you’re involved with these engines, get ready for smoother rules and make sure to share your thoughts by August 14, 2026!
Analyzed Economic Effects
3 provisions identified: 2 benefits, 1 costs, 0 mixed.
New SI Engines Face NSPS Limits
Although the exemption covers both new and existing SI stationary engines, new SI engines that qualify for the exemption will still be subject to the more stringent NOX emission limits in the New Source Performance Standards at 40 CFR part 60, subpart JJJJ. That means newly installed SI engines in Missouri must meet the NSPS NOX limits even if they meet the 25‑ton seasonal threshold.
25‑Ton NOX Exemption for SI Engines
Missouri added an exemption for spark‑ignited (SI) stationary engines that emit 25 tons or less of NOX during the ozone season (May 1 through September 30). Engines that meet this 25‑ton seasonal threshold will not have to follow the rule's general provisions, including its emission limits and the testing requirements in section (5)(A).
Simplified Reporting and Definitions
Missouri reformatted and revised reporting, recordkeeping, and test method requirements (found in sections (4)(A) and (5)), added definitions that match 10 CSR 10-6.020 or 40 CFR 60.4219, and corrected incorrect rule references. These changes aim to simplify compliance paperwork and clarify requirements for affected engines.
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