This paper seeks to determine the efficacy of California’s Smog Check Program. The Smog Check Program regulates vehicle emissions by requiring biennial emissions testing. Between 2010 and 2017, California’s fine particulate pollution level average was 22.7% higher than the next leading state, and 41.7% higher than the national average, leading them to implement and enforce emissions testing for vehicles to control pollutants (US EPA & US Census Bureau, n.d.). Heightened smog levels carry significant risk to humans and the environment, making them a major concern (Romley et al., 2010). In this paper I use Multiple Regression and Synthetic Controls methods to analyze the trends in vehicular pollutants across California counties with differing levels of stringency of the Smog Check Program over time. The results of both methods show that there was not a significant change in vehicle related pollutants between the county that increased its program stringency to a higher level and the control groups that did not change.