<p>More exposure assessment and epidemiological studies are needed for PM₁, a health-relevant but understudied pollutant, to better understand and mitigate its health risks. This study conducted a 3.5-year PM₁ monitoring campaign in a mountainous community, where air pollutants are more easily trapped, using research-grade low-cost sensors, namely, AS-LUNG-O sets. Nine solar-powered AS-LUNG-O sets were installed at street level, with an additional unit positioned 10&#xa0;m above the ground to serve as an ambient reference. Street-level sensors were placed 3–5&#xa0;m from potential sources such as traffic, temples, and vendors. During the 3.5-year period, the overall mean PM₁ concentration across the nine street-level locations was 20.9 ± 11.0&#xa0;μg/m³, compared to 17.0 ± 8.4&#xa0;μg/m³ at the elevated site. PM₁ levels were typically higher in winter and on religious days across all locations. Spatial analysis revealed that PM₁ hot spots varied by season, day of the week (weekday vs. weekend), and event type (religious vs. typical days). These hot spots were commonly located near traffic sources, temples, and markets. Notably, most of the maximum PM₁ values across the ten locations occurred on weekdays and typical days, highlighting the unpredictable nature of PM₁ levels influenced by community events. Source contributions to PM₁ were estimated using a generalized additive mixed model; the PM₁ contribution from religious events, traffic, and vendors reached statistical significance. The identified hot spots and source contributions can inform targeted control strategies addressing local pollution sources. This study offers a more representative assessment of PM₁ exposure for local residents than data from ambient monitoring stations or short-term monitoring campaigns. The methodology presented can also be applied in other countries to support community-based PM₁ studies.</p> Graphical abstract <p></p>