EPA OKs Missouri's Smog-Cutting Engine Rule Updates
Published Date: 10/1/2026
Rule
Summary
The EPA is giving a thumbs-up to Missouri’s updated rules for big stationary engines that cut down on smog-causing nitrogen oxide (NOX) pollution. These changes simplify paperwork, clear up confusing language, and even exempt some spark-ignited engines. Starting November 2, 2026, affected businesses will follow these smoother, smarter rules—helping clean air without extra hassle or surprise costs.
Analyzed Economic Effects
4 provisions identified: 3 benefits, 1 costs, 0 mixed.
Reporting and Recordkeeping Simplified
Missouri revised 10 CSR 10-6.390 to reformat and revise reporting, recordkeeping, and compliance requirements for large stationary internal combustion engines. These changes (effective November 2, 2026) are intended to simplify paperwork and clarify language for businesses subject to the rule.
Exemption for Certain Spark‑Ignited Engines
The approved Missouri rule revisions add an exemption for certain spark-ignited internal combustion engines, meaning owners/operators of those exempt engines in Missouri will not be subject to the rule's requirements starting November 2, 2026.
State Rule Now Federally Enforceable
The EPA incorporated Missouri's 10 CSR 10-6.390 into the Federal SIP, making the rule federally enforceable under Clean Air Act sections 110 and 113 as of November 2, 2026.
No Significant Economic Impact on Small Entities
The EPA certified under the Regulatory Flexibility Act that this SIP approval does not have a significant economic impact on a substantial number of small entities.
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