Impact of air purifiers on occupational particle exposure in an enclosed bus workshop

• Bus workshops show elevated fine (PM2.5) and ultrafine particle (UFP) levels. • Air purifiers reduced PM2.5, PM4, and PM10 by 45%, 49%, and 53% across shifts. • Elemental carbon decreased by 46%, while BC and OC removal remained negligible. • Purifier efficiency peaked at 60% for coarse particles (10 µm). • Air purifiers were less effective for UFPs and semi-volatile organics. Workers in bus workshops are exposed to elevated concentrations of fine (PM 2.5 , <2.5 µm) and ultrafine particles (UFP, <0.1 µm) from diesel exhaust, brake and tire wear, and mechanical operations, which are associated with adverse respiratory and cardiovascular outcomes. To characterize exposures and evaluate mitigation strategies, two measurement campaigns were conducted in a bus workshop. Particle number concentrations (PNC), size distributions, black carbon (BC), elemental and organic carbon (EC/OC), and particulate mass (PM 2.5 , PM 4 , PM 10 ) were monitored at near field, breathing zones, and far field locations during maintenance tasks. The first campaign established baseline conditions, while the second assessed the impact of four air purifiers (APs). Baseline monitoring showed exposure peaks during high-emission activities such as brake servicing, and cold engine starts, with PNCs reaching 4.5 × 10 5 cm -3 and PM 4 up to 549 µg m -3 . While gravimetric concentrations remained below mass-based occupational exposure limits, UFPs and EC exceeded precautionary health benchmarks. The use of APs increased the effective air exchange rate and reduced PNCs (<700 nm) by 38%, and PM 2.5 , PM 4 , and PM 10 by 45%, 49%, and 53%, respectively. EC decreased by 46%, whereas BC and OC showed negligible changes. Size-resolved analysis confirmed highest removal efficiency for coarse particles (60% at 10 µm) and lowest (33%) within 300-700 nm range, the most penetrating particle size. This study demonstrates that bus workshops present clear risks of occupational particle exposure, and that APs can significantly reduce concentrations, though limitations remain for UFPs and semi-volatile organics.