Organic and elemental carbon concentrations in carbonaceous aerosols during summer and winter sampling campaigns in Barcelona, Spain

Daily PM10 and PM2.5 samples were collected at an urban background monitoring site in Barcelona (Spain) in summer and winter 2004. The instrumentation used consisted of two high-volume (PM10 and PM2.5) and two low-volume samplers (PM2.5), one of them coupled to an annular diffusion denuder aiming to evaluate the influence of sampling artefacts related to the adsorption of volatile carbonaceous species. Quartz fibre filters of 15 cm and 47 mm diameter were used as collection substrates (Schleicher & Schuell QF20 and Whatman QM-A, respectively). The resulting samples were analysed for organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC). Total carbon (TC) was calculated as OC+EC. The present study aimed to (a) determine maximum (winter) and minimum (summer) OC/EC/TC/WSOC levels in the study area, and (b) assess the magnitude and influence of positive sampling artefacts. Mean levels of TC in PM2.5 ranged from 4 to 5 μg m−3 in summer to 7–10 μg m−3 in winter with the different samplers (5 and 8 μg m−3, respectively, in PM10, one sampler); OC levels in PM2.5 were 3–4 μg m−3 in summer and 6–7 μg m−3 in winter (4 and 6 μg m−3 in PM10); EC levels in PM2.5 ranged from 1 to 2 μg m−3 in summer to 1–3 μg m−3 in winter (1 and 2 μg m−3 in PM10). Thus, OC/EC/TC winter levels were higher than summer levels by a factor of 1.7–2. WSOC levels were 1.6 μg m−3 in PM2.5 and PM10 in summer, and 2.1 μg m−3 (PM2.5) and 1.9 μg m−3 (PM10) in winter. The results indicate that positive artefacts for OC accounted for 0.5–0.7 μg m−3, representing 11–16% of the raw OC mass and 3% of the PM2.5 mass. Sampling artefacts for OC were slightly higher in summer. EC levels were similar for the low-volume samplers and unusually low for the high-volume samplers, suggesting that EC determination could be influenced by the filter type.