<p>Sarnia, ON experiences pollutant emissions disproportionate to its relatively small size. The small size of the city limits traditional top-down emission estimate techniques (e.g., satellite) but a low-cost solution for emission monitoring is Mobile-MAX-DOAS. Measurements were made using this technique from 21/03/2017 to 23/03/2017 along various driving routes to retrieve vertical column densities (VCDs) of NO<sub>2</sub> and SO<sub>2</sub> and to estimate emissions of NO<sub><i>x</i></sub> and SO<sub>2</sub> from the Sarnia region. A novel aspect of the current study was the installation of a NO<sub><i>x</i></sub> analyzer in the vehicle to allow real time measurement and characterization of near-surface NO<sub><i>x</i></sub>/NO<sub>2</sub> ratios across the urban plumes, allowing improved accuracy of NO<sub><i>x</i></sub> emission estimates. Confidence in the use of near-surface measured NO<sub><i>x</i></sub>/NO<sub>2</sub> ratios for estimation of NO<sub><i>x</i></sub> emissions was increased by relatively well-mixed boundary layer conditions. These conditions were indicated by similar temporal trends in NO<sub>2</sub> VCDs and mixing ratios when measurements were sufficiently distant from the sources. Leighton ratios within transported plumes indicated peroxy radicals were likely disturbing the NO-NO<sub>2</sub>-O<sub>3</sub> photostationary state through VOC oxidation. The average lower limit emission estimate of NO<sub><i>x</i></sub> from Sarnia was 1.60 ± 0.34 tonnes hr<sup>−1</sup> using local 10 m elevation wind-speed measurements. Our estimates were larger than the downscaled annual 2017 NPRI reported industrial emissions of 0.9 tonnes NO<sub><i>x</i></sub> hr<sup>−1</sup>. Our lower limit estimate of SO<sub>2</sub> emissions from Sarnia was 1.81 ± 0.83 tonnes SO<sub>2</sub> hr<sup>−1</sup>, equal within uncertainty to the 2017 NPRI downscaled value of 1.85 tonnes SO<sub>2</sub> hr<sup>−1</sup>. Satellite-derived NO<sub>2</sub> VCDs over Sarnia from the Ozone Monitoring Instrument (OMI) were lower than Mobile-MAX-DOAS VCDs, likely due to the large pixel size relative to the city’s size. The results of this study support the utility of the Mobile-MAX-DOAS method for estimating NO<sub><i>x</i></sub> and SO<sub>2</sub> emissions in relatively small, highly industrialized regions especially when supplemented with mobile NO<sub><i>x</i></sub> measurements.</p>