Williams Transmissions and Express Smog
Ronald Hennion
MobileOBDMotor Home
Clean Truck Check in Napa, CA
13 credentialed testers in Napa.
Testers in Napa
C.A.R.B CREDENTIALED TESTER- MOBILE TESTING
Sam Nikoto
MobileOBDOVIOVI tests are required for 2012 and older enginesMotor Home
Steve DiPiero
MobileOBDOVIOVI tests are required for 2012 and older engines
Trucking activity in Napa County
Clean Truck Check applies to heavy-duty vehicles that operate in California — including out-of-state trucks based here that run loads west.
Trucking establishments
34
Trucking employees
234
Source: FMCSA MCMIS carrier census, US Census County Business Patterns 2021.
Air quality context in and around Napa
Annual aggregate readings from EPA Air Quality System monitors within about 25 miles of Napa, reporting year 2025. Clean Truck Check exists to reduce real-world emissions from heavy-duty vehicles — the numbers below are the local baseline those rules are designed to improve.
Ozone (O₃)
0.04 Parts per million
1 monitor · 31,897 observations · 0 days above standard
Source: EPA Air Quality System (AQS) API. Reporting year 2025. Last fetched 2026-05-18.