<p>Particulate matter (PM) poses a significant public health concern, particularly in industrialized communities. While modern sophisticated air monitors like those deployed by the United States Environmental Protection Agency (US EPA) provide accurate 24-h PM2.5 (PM ≤ 2.5&#xa0;µm) data, limited spatial and temporal coverage may create monitoring gaps. Low-cost monitors, such as a PurpleAir monitor (PA-II), offer an accessible alternative; however, their accuracy can be influenced by local environmental conditions and PM characteristics. This study evaluated the site-specific performance of PA-II in an industrial region within northern Lake County (N = 6) and a suburban region of Tippecanoe County (N = 4), both in Indiana, United States. As a reference measurement, a deployable particulate sampler (DPS) was co-located with each PA-II. For microscopic analysis, PM was collected on a glass substrate. PA-II data were assessed in raw form and following calibration using two methods, with performance assessed by root mean square error (RMSE) and the coefficient of determination (R²). Microscopic analysis revealed the presence of dark, irregular particles near industrial sites in northern Lake County, which may affect sensor readings by altering light-scattering efficiency. Raw PA-II data showed weak absolute agreement with DPS measurements in northern Lake County (RMSE: 2.04&#xa0;µg/m³, R²: 0.25), while the US-wide calibration exhibited the best performance (RMSE: 1.40&#xa0;µg/m³; R²: 0.67). In contrast, raw data showed the best performance in Tippecanoe County (RMSE: 0.62&#xa0;µg/m³; R²: 0.94). These findings highlight the relevance of site-specific calibration approaches to enhance the accuracy of low-cost PM2.5 monitors, especially in environmentally impacted communities.</p> Graphical Abstract <p></p>