Size distribution and sources of trace metals and n-alkanes in the Athens urban aerosol during summer

Size-resolved, 24-h aerosol samples were collected from June–July 2001 by means of an Andersen high-volume cascade impactor. Sampling was conducted in a central avenue (Patission) characterised by heavy traffic, 21 m above street level, in the Athens city centre. Samples were analysed by atomic absorption spectrometry and gas chromatography to determine the size distribution of nine metallic elements (Cd, Pb, V, Ni, Mn, Cr, Cu, Fe, Al) and n-alkanes (with carbon numbers in the range 18–35). The aerosol mass median diameter (MMD) was calculated by means of probit analysis on the cumulative mass concentration size distribution for each metals and n-alkane. The total n-alkane mass concentration (TNA) in total suspended particles (TSP) ranged from 72 to 1506 ng m−3 while the total metal concentration ranged from 5.6 to 28.6 μg m−3. The results showed that metals such as Cd, V and Ni are characterised by a MMD <1 μm, while the MMD for Pb and Mn are 1 μm. Such metals are generally considered to have anthropogenic emission sources. Other metals such as Al, Fe, Cu and Cr were found to have MMD=2–6 μm, which generally originate from soil dust or mechanical abrasion processes. The Carbon number profile of n-alkane compounds showed a strong anthropogenic source with only a minor biogenic influence. The concentration of most n-alkanes was characterised by high variability during the sampling period, in contrast to the concentration of most trace metals. Most n-alkanes had a unimodal size distribution with MMD=1–2 μm similar to those of some trace metals (Pb, Mn), which originate mostly from vehicle emissions. This is a strong indication that these species have a common source. Finally, gas–particle partitioning of n-alkanes was also examined for different particle sizes by means of the relationship between the partition constant Kp and saturation vapour pressure (pL0) as proposed by current sorption models.