Online Training & Materials Estimated Emission Reductions from California’s Enhanced Smog Check Program Share SHARE Facebook share Twitter LinkedIn Copy URL Email Download Download es0208759 en Added on: 02 March, 2026 Breadcrumb Home Resource Library Estimated Emission Reductions From California’s Enhanced Smog Check Program This Environmental Science & Technology paper estimates emission benefits of California’s Enhanced Smog Check program around 1999, using a “bottom-up” approach combining per-vehicle emission-rate reductions with activity by model year.It is a frequently cited evidence source for quantifying how inspection and maintenance programs can reduce tailpipe emissions from the in-use fleet when well-designed and enforced.