Chemical composition of PM₁₀ at a rural site in the western Mediterranean and its relationship with the oxidative...

A comprehensive chemical characterization (water-soluble ions, organic and elemental carbon, water- and methanol-soluble organic carbon, levoglucosan, and major and trace metals) of PM₁₀ samples collected in a rural area located in the southeast of the Iberian Peninsula was performed. Additionally, the oxidative potential of the samples, used as an indicator of aerosol toxicity, was determined by the ascorbic acid (OP^AA) and dithiothreitol (OP^DTT) assays. The average concentration of PM₁₀ during the study period, spanning from late winter to early spring, was 20.2 ± 10.8 μg m^-3. Nitrate, carbonate and calcium (accounting for 20% of the average PM₁₀ mass concentration) and organic matter (with a contribution of 28%) were the main chemical components of PM₁₀. Average concentrations of traffic tracers such as elemental carbon, copper and zinc (0.31 μg m^-3, 3 ng m^-3, and 9 ng m^-3, respectively) were low compared with those obtained at an urban site in the same region, due to the almost total absence of traffic in the surrounding of the sampling site. Regarding levoglucosan and K⁺, which can be considered as tracers of biomass burning, their concentrations (0.12 μg m^-3 and 55 ng m^-3, respectively) were in the lower range of values reported for other rural areas in Europe, suggesting a moderate contribution form this source to PM₁₀ levels. The results of the Pearson's correlation analysis showed that volume-normalised OP^AA and OP^DTT levels (average values of 0.11 and 0.32 nmol min^-1 m^-3, respectively) were sensitive to different PM₁₀ chemical components. Whereas OP^AA was not strongly correlated with any of the species measured, good correlation coefficients of OP^DTT with water-soluble organic carbon (r = 0.81) and K⁺ (r = 0.73) were obtained, which points to biomass burning as an important driver of the DTT activity.