Urban particulate pollution (PM2.5, PM10) poses significant health risks. Green roofs (vegetated rooftops) are known to mitigate urban heat and manage stormwater, but their direct local air-quality benefits are not well quantified. This study addresses that gap by quantifying particulate matter reductions from a green roof using a high-resolution paired sensor approach. We conducted a high-resolution paired-sensor field experiment to measure particulate matter concentrations on a green roof versus a nearby control roof. Identical sensors concurrently monitored PM2.5 and PM10 at minute-level resolution. The collected data were analyzed for overall differences, diurnal variation (nighttime versus daytime), and wind-dependent effects, using paired statistical tests to determine significance. Mean PM2.5 concentration over the green roof was 0.095 μg/m3 (4.9%) lower than the control, and PM10 was 0.103 μg/m3 (5.1%) lower; both differences were statistically significant (p < 0.01). The green roof’s PM reduction was greater at night (0.18 μg/m3) than during daytime (0.04 μg/m3), and strongest under calm winds (<0.5 m/s, 0.16–0.18 μg/m3). The results indicated that green roofs can provide tangible local air-quality improvements. The observed small yet significant PM reductions demonstrate that vegetated roofs contribute to cleaner air at the building scale. These findings support the integration of green roofs into green building design and urban climate resilience strategies, adding air-quality enhancement to their known co-benefits.