Vertical and horizontal variability of PM₁₀ source contributions in Barcelona during SAPUSS

Abstract

During the SAPUSS campaign (Solving Aerosol Problems by Using Synergistic Strategies) PM10 samples at 12-hour resolution were simultaneously collected at four monitoring sites located in the urban agglomerate of Barcelona (Spain). A total of 221 samples were collected from 20 September to 20 October 2010. The Road Site (RS) site and the Urban Background (UB) site were located at street level, whereas the Torre Mapfre (TM) and the Torre Collserola (TC) sites were located at 150 m a.s.l. by the sea side within the urban area and at 415 m a.s.l. 8 km inland, respectively. For the first time, we are able to report simultaneous PM10 aerosol measurements, allowing us to study aerosol gradients at both horizontal and vertical levels. The complete chemical composition of PM10 was determined on the 221 samples, and factor analysis (positive matrix factorisation, PMF) was applied. This resulted in eight factors which were attributed to eight main aerosol sources affecting PM10 concentrations in the studied urban environment: (1) vehicle exhaust and wear (2–9 µg m−3, 10–27 % of PM10 mass on average), (2) road dust (2–4 µg m−3, 8–12 %), (3) mineral dust (5 µg m−3, 13–26 %), (4) aged marine (3–5 µg m−3, 13–20 %), (5) heavy oil (0.4–0.6 µg m−3, 2 %), (6) industrial (1 µg m−3, 3–5 %), (7) sulfate (3–4 µg m−3, 11–17 %) and (8) nitrate (4–6 µg m−3, 17–21 %). Three aerosol sources were found to be enhanced at the ground levels (confined within the urban ground levels of the city) relative to the upper levels: (1) vehicle exhaust and wear (2.8 higher), (2) road dust (1.8 higher) and (3) local urban industries/crafts workshops (1.6 higher). Surprisingly, the other aerosol sources were relatively homogeneous at both horizontal and vertical levels. However, air mass origin and meteorological parameters also played a key role in influencing the variability of the factor concentrations. The mineral dust and aged marine factors were found to be a mixture of natural and anthropogenic components and were thus further investigated. Overall, three types of dust were identified to affect the urban study area: road dust (35 % of the mineral dust load, 2–4 µg m−3 on average), Saharan dust (28 %, 2.1 µg m−3) and background mineral dust (37 %, 2.8 µg m−3). Our results evidence that although the city of Barcelona broadly shows a homogeneous distribution of PM10 pollution sources, non-exhaust traffic, exhaust traffic and local urban industrial activities are major coarse PM10 aerosol sources.