Size-distribution of particulate saccharides at a coastal site in the South Western Mediterranean during the ChArMEx experiment: sources and formation processes
摘要
As part of the Chemistry and Aerosols Mediterranean Experiment (ChArMEx), aerosol samples were collected from the western side of the Mediterranean basin from July to November of 2012 and investigated for anhydrosaccharides, sugar-alcohols, and monosaccharides to learn more about their possible origins and how they arise. Saccharides are ubiquitous chemicals in terrestrial and marine habitats. As part of the Chemistry and Aerosols Mediterranean Experiment (ChArMEx), the size distribution (6 sizes, from 0.49 to 10 µm) of saccharides was investigated in the western Mediterranean basin from July to November 2012. The origins and formation processes of anhydrosaccharides, sugar-alcohols, and monosaccharides were studied. The concentration levels of furfural as a potential tracer for biomass combustion were also determined. The average concentration of the total saccharides was 215.7 ± 84.3 ng m−3. Anhydrosaccharides had the highest concentration, followed by sugar-alcohols and monosaccharides, among the several saccharide groups. Levoglucosan was the most abundant saccharide (117 ng m−3, 36.9–258.8 ng m−3). For both coarse and fine modes, levoglucosan predominated among anhydrosaccharides, and arabitol prevailed among sugar-alcohols; mannose was the most abundant in the coarse mode, while glucose was the most abundant in the fine mode for monosaccharides. A bimodal size distribution analysis of levoglucosan and mannosan revealed a fine mode peak at 0.95–3 µm, indicating a biomass-burning origin consolidated by a strong Pearson correlation (r = 0.85, p-value < 0.001). Sugar-alcohols (arabitol and mannitol) showed a bimodal size distribution trend with a significant peak in the coarse mode. The three monosaccharides (glucose, galactose, and mannose) showed a bimodal size distribution trend with a significant peak at coarse mode for glucose and galactose and an unimodal distribution for mannose. Based on the principal component analysis (PCA), the fourth factor explained 88.2% of the study's variance. The PCA results showed that bioaerosols and biomass burning accounted for much of the aerosol. At the same time, fungal spores and vegetative soil were the main sources of the measured aerosol sample. The polluted air masses traversed Europe and proceeded east over Algeria to the Mediterranean Sea, which is likely to impact the southwestern region of the Mediterranean significantly.