An oxidizing and harmful pollutant gas, tropospheric ozone is a product of a complex set of photochemical reactions that can make it difficult to enact effective control measures. A better understanding of its precursors including volatile organic compounds (VOCs) and nitrogen oxides (NO
x) and their spatial distribution can enable policymakers to focus their control efforts. In this study we used low-cost sensors (LCSs) to increase the spatial resolution of an existing NO
2 monitoring network in addition to VOC sampling to better understand summer ozone formation in Maricopa County, Arizona, and observed that afternoon O
3 values at the downwind sites were significantly correlated, ~0.27, to the morning NO
2 × rate values at the urban sites. Additionally, we looked at the impact of wildfire smoke on ozone exceedances and compared non-smoke days to smoke days. The average O
3 on smoke days was approximately 20% higher than on non-smoke days, however, the average NO
2 concentration multiplied by estimated photolysis rate (NO
2 × rate) values were only 2% higher on smoke days. Finally, we evaluated the ozone sensitivity of the region by calculating HCHO/NO
2 ratios using three different datasets: ground, satellite, and model. Although the satellite dataset produced higher HCHO/NO
2 ratios than the other datasets, when the proper regime thresholds are applied the three datasets consistently show transition and VOC-limited O
3 production regimes over the Phoenix metro area. This suggests a need to implement more VOC emission controls in order to reach O
3 attainment in the county.
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