Regulatory Rollback and the Smoking Tailpipe: Air-Quality Effects of Repealing Vehicle Emissions Testing

Regulatory Rollback and the Smoking Tailpipe: Air-Quality Effects of Repealing Vehicle Emissions Testing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Regulatory Rollback and the Smoking Tailpipe: Air-Quality Effects of Repealing Vehicle Emissions Testing Nicholas A. Jensen, Patricia J. Hummel, Nicholas Reinarts This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8753461/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract A growing number of states have repealed mandatory vehicle emissions testing, arguing that advances in vehicle technology and overlapping environmental regulations render such programs redundant while imposing unnecessary costs on drivers. We evaluate this claim by estimating the air-quality effects of emissions-testing repeal using a newly constructed county-by-year dataset of testing requirements linked to U.S. Environmental Protection Agency air-quality data from 1990–2019. Using a staggered policy design, we compare counties that repeal testing to counties that never repeal. We implement three counterfactual-imputation approaches that predict untreated outcomes from pre-repeal trends and contemporaneous untreated counties, allowing us to assess model fit, identifying assumptions, and sensitivity. Our primary matrix-completion specification estimates an average increase in median AQI of 4.7 points, with secondary outcomes showing corresponding shifts in the distribution of air-quality categories. These results are robust across alternative estimators. We evaluate credibility using pre-treatment predictive fit, placebo-style diagnostics, leave-one-out validation, and formal sensitivity analysis that allows limited departures from parallel trends. Overall, emissions-testing repeal is associated with worse air quality on average, with larger effects among earlier repealers and more heterogeneous effects among later cohorts, indicating that nominally "redundant" regulations can remain environmentally consequential. JEL Classification: Q58 , Q53 , C23 , Q52 , K32 Regulatory rollback Environmental regulation Vehicle emissions testing Air quality Regulatory obsolescence Counterfactual policy evaluation Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 28 Mar, 2026 Reviews received at journal 26 Mar, 2026 Reviews received at journal 03 Mar, 2026 Reviewers agreed at journal 27 Feb, 2026 Reviewers agreed at journal 26 Feb, 2026 Reviewers invited by journal 26 Feb, 2026 Editor assigned by journal 04 Feb, 2026 Submission checks completed at journal 04 Feb, 2026 First submitted to journal 31 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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We evaluate this claim by estimating the air-quality effects of emissions-testing repeal using a newly constructed county-by-year dataset of testing requirements linked to U.S. Environmental Protection Agency air-quality data from 1990–2019. Using a staggered policy design, we compare counties that repeal testing to counties that never repeal. We implement three counterfactual-imputation approaches that predict untreated outcomes from pre-repeal trends and contemporaneous untreated counties, allowing us to assess model fit, identifying assumptions, and sensitivity. Our primary matrix-completion specification estimates an average increase in median AQI of 4.7 points, with secondary outcomes showing corresponding shifts in the distribution of air-quality categories. These results are robust across alternative estimators. 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