{"id":335,"date":"2026-04-28T11:52:19","date_gmt":"2026-04-28T11:52:19","guid":{"rendered":"https:\/\/marinersupdate.com\/blog\/?p=335"},"modified":"2026-04-28T11:52:19","modified_gmt":"2026-04-28T11:52:19","slug":"updated-scr-compliance-framework-revised-nox-monitoring-requirements-effective-may-2026","status":"publish","type":"post","link":"https:\/\/marinersupdate.com\/blog\/updated-scr-compliance-framework-revised-nox-monitoring-requirements-effective-may-2026\/","title":{"rendered":"Updated SCR Compliance Framework: Revised NOx Monitoring Requirements Effective May 2026"},"content":{"rendered":"\n<h3 class=\"wp-block-heading\"><strong>Overview of Regulatory Update<\/strong><\/h3>\n\n\n\n<p>Significant revisions to the Selective Catalytic Reduction (SCR) framework will come into effect on <strong>1 May 2026<\/strong>. These updates introduce a new approach to evaluating NOx measurement performance, particularly in relation to catalyst monitoring. The previously defined \u00b15% accuracy benchmark has been removed and replaced with a broader requirement for \u201csufficient accuracy,\u201d shifting more responsibility onto system applicants.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Applicability of the New Rules<\/strong><\/h3>\n\n\n\n<p>These updated provisions apply to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Marine diesel engines installed on ships with a keel laid on or after <strong>1 November 2025<\/strong>, or<\/li>\n\n\n\n<li>Ships delivered on or after <strong>1 May 2026<\/strong><\/li>\n<\/ul>\n\n\n\n<p>The <strong>2025 SCR Guidelines (Resolution MEPC.399(83))<\/strong> officially replace the earlier <strong>2017 SCR Guidelines (MEPC.291(71))<\/strong>, introducing revised expectations for NOx monitoring systems.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Changes in NOx Measurement Expectations<\/strong><\/h3>\n\n\n\n<p>Under earlier guidelines, NOx monitoring devices were required to demonstrate an accuracy of \u00b15% when compared to a certified reference analyzer (such as a chemiluminescence detector compliant with NTC 2008 standards).<\/p>\n\n\n\n<p>With the 2025 update:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The fixed \u00b15% accuracy requirement has been eliminated.<\/li>\n\n\n\n<li>NOx measurement systems must now demonstrate <strong>\u201csufficient accuracy\u201d<\/strong> for effectively tracking catalyst condition and degradation.<\/li>\n\n\n\n<li>No explicit numerical threshold has been defined, leaving interpretation open.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>What This Means for Applicants<\/strong><\/h3>\n\n\n\n<p>The absence of a strict accuracy benchmark means applicants must now:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Justify that their NOx monitoring system provides reliable data for assessing catalyst health.<\/li>\n\n\n\n<li>Demonstrate acceptable deviation levels between onboard instruments and reference analyzers.<\/li>\n\n\n\n<li>Consider factors such as:\n<ul class=\"wp-block-list\">\n<li>Instrument precision and inherent accuracy<\/li>\n\n\n\n<li>Long-term measurement drift<\/li>\n\n\n\n<li>Proximity to regulatory NOx limits<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p>Additionally, applicants should ensure that not only the raw NOx readings (e.g., ppm values) are reliable, but also that the <strong>methodology used to interpret these readings<\/strong> is robust and defensible.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Technical Considerations for Measurement Reliability<\/strong><\/h3>\n\n\n\n<p>Measurement accuracy is influenced by more than just the analyzer itself. Key aspects include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Sampling location<\/strong> within the exhaust system<\/li>\n\n\n\n<li><strong>Exhaust gas mixing quality<\/strong> at the sampling point<\/li>\n<\/ul>\n\n\n\n<p>These elements must be carefully evaluated and validated during system testing and verification.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Implementation Guidance<\/strong><\/h3>\n\n\n\n<p>To align with the updated SCR Guidelines, stakeholders should:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Review and revise existing <strong>Technical Files<\/strong> for individual engines and engine families<\/li>\n\n\n\n<li>Incorporate the new requirements into <strong>parent engine emission testing plans<\/strong><\/li>\n\n\n\n<li>Update supporting documentation for future engine certifications<\/li>\n<\/ul>\n\n\n\n<p>An accompanying appendix (referenced in the original guidance) provides additional recommendations for practical implementation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Reference Standard<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>IMO Resolution MEPC.399(83)<\/strong>\u2013 <em>2025 Guidelines on Selective Catalytic Reduction (SCR) Systems<\/em><\/li>\n<\/ul>\n\n\n\n<div data-wp-interactive=\"core\/file\" class=\"wp-block-file\"><object data-wp-bind--hidden=\"!state.hasPdfPreview\" hidden class=\"wp-block-file__embed\" data=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/04\/SCR-COMPLIANCE.pdf\" type=\"application\/pdf\" style=\"width:100%;height:600px\" aria-label=\"Embed of SCR COMPLIANCE.\"><\/object><a id=\"wp-block-file--media-c3e869fc-5ce2-4f0c-b3ec-12e1a0384f05\" href=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/04\/SCR-COMPLIANCE.pdf\">SCR COMPLIANCE<\/a><a href=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/04\/SCR-COMPLIANCE.pdf\" class=\"wp-block-file__button wp-element-button\" download aria-describedby=\"wp-block-file--media-c3e869fc-5ce2-4f0c-b3ec-12e1a0384f05\">Download<\/a><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Overview of Regulatory Update Significant revisions to the Selective Catalytic Reduction (SCR) framework will come into effect on 1 May 2026. These updates introduce a new approach to evaluating NOx measurement performance, particularly in relation to catalyst monitoring. The previously defined \u00b15% accuracy benchmark has been removed and replaced with [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":337,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[431,424,426,432,428,12,434,253,233,427,430,425,213,433,429],"class_list":["post-335","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-imo-solas-marpol-stcw-loadline-ism-isps-statutory","tag-cleantechnology","tag-dieselengine","tag-emissionscontrol","tag-engineeringinnovation","tag-environmentalcompliance","tag-imo","tag-industrialengineering","tag-marineengineering","tag-maritime-2","tag-noxreduction","tag-regulatoryupdate","tag-scrsystems","tag-shippingindustry","tag-shiptechnology","tag-sustainableshipping"],"_links":{"self":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/335","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/comments?post=335"}],"version-history":[{"count":1,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/335\/revisions"}],"predecessor-version":[{"id":338,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/335\/revisions\/338"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/media\/337"}],"wp:attachment":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/media?parent=335"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/categories?post=335"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/tags?post=335"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}