<p>U.S. Environmental Protection Agency (EPA) monitors are crucial for standardized air quality measurements but often fall short in coverage, leaving many areas without adequate monitoring. The growing network of low-cost sensors, such as PurpleAir for small (&lt; 2.5 µm) particulate matter (PM_2.5), can help fill these gaps and provide a comprehensive understanding of exposure. Our study examines the spatial distribution of governmental (EPA) and non-governmental (PurpleAir) air quality networks in Maricopa County, Arizona, by integrating socio-demographic data from the American Community Survey at the census tract level. We utilized Wilcoxon rank-sum tests and multivariable generalized estimating equations to evaluate the relationship between sensor presence and socio-demographic characteristics. Results revealed that census tracts with EPA regulatory monitors have a higher percentage of Hispanic and foreign-born residents and lower median household incomes. Census tracts with PurpleAir sensors have a significantly higher percentage of White and Asian residents and higher median household income compared to those without sensors. Our multivariable models suggest that the presence of PurpleAir sensors is positively associated with the percentage of Asian residents and median household income but is negatively associated with the percentage of foreign-born residents. Using bivariate local indicators of spatial autocorrelation analysis, we identified 171 census tracts with high percentages of foreign-born residents and no PurpleAir sensors and 247 census tracts with low median household income and no PurpleAir sensors. Findings underscore the need for strategic deployment of low-cost sensors to address gaps in air quality monitoring, which can inform and support environmental justice initiatives in underserved communities.</p>