Outdoor and indoor measurements of number particles size distributions and equivalent black carbon (EBC) at a mechanical manufacturing plant

Human exposure to air pollution is of great concern, especially in working places, where many people spend a lot of time. This work describes results obtained during a measurements campaign (February–July 2021) of aerosol number size distributions and equivalent black carbon (EBC), inside and outside a mechanical manufacturing plant, in Southern Italy. Outdoor and indoor EBC data are highly correlated (R2 = 0.98) suggesting the same sources: vehicular traffic, domestic heating and agricultural waste burning (February–April). In these months the outdoor Angstrom absorption exponent (AAE) was highly oscillating (0.64–1.62), with reduced oscillations (0.9–1.5) during warmer months. These last values suggest the influence of a diffuse cloud of aged smoke due to uncontrolled and extended wheat biomass burning, lasting about one month, in the nearby Apulia region. A good correlation between outdoor EBC and NC1 (particles number with D ≤ 1 μm) confirms that EBC has a high contribution to the aerosol size distribution. The same profile of number size distributions in both configurations indicates the same sources but, during cold months, the outdoor ones are characterized by higher values than the warm months, especially in the fine particles range. During working and non-working days, a reduction of indoor particles number concentration over the whole size range is observed throughout the weekend, suggesting manufacturing activities as one of the sources. Scanning electron microscope (SEM) analysis of outdoor and indoor spare internal filters shows the presence of metal particles indicating inside particles are being transported outside.