Tracing of aerosol sources in an urban environment using carbonaceous, major ions, Sr isotope, and mineralogical compositional data

Abstract

Understanding the chemical composition of atmospheric particulate matter (PM), particularly with a diameter less than 2.5 μm (PM2.5), has became an emergent topic in atmospheric research due to its relation to climate change and serious health issues. In this study, a comprehensive assessment of the carbonaceous (organic carbon, water-soluble organic carbon, elemental carbon), major water-soluble inorganic ions (SO42-, NO3-, NH4+, Cl-, K+, Na+), 86Sr/87Sr isotope ratios, and mineralogical composition of PM2.5 samples has been performed for a one-year period in an urban environment at the Western European Coast (Aveiro, Portugal). The concentration of each component was found to be highly dependent on the seasonal events, with the carbonaceous component being the major constituent of the PM2.5 in almost all seasons. The concentration of SO42- is higher in samples collected during warm seasons than in those of colder seasons, which is indicative of secondary formation (mediated by sunlight) in the atmosphere [F. Zhang et al., 2014]. On the other hand, the concentration of the more volatile NO3- ion is highest for samples collected in colder seasons, which can be explained by the combined effects of lower air temperature and an increase of biomass burning and vehicles emissions during these seasons [F. Zhang et al., 2014] . The equivalent molar ratio of cations to anions was also computed, indicating that the PM2.5 is more acidic during high air temperature periods probably due to the highest accumulation of acidic components (e.g., SO42-) during this period [J. Zhang et al., 2014]. For the 86Sr/87Sr isotope ratios, it was possible to distinguish the labile (acid-leached) from the natural (remaining residue) Sr components (Fig.1). The highest 86Sr/87Sr ratios were observed for the residues embedded in the collection medium, being this indicative of a natural crustal dust source. The 86Sr/87Sr isotope ratios verified for the leachates are of the same order of magnitude of the reference value for seawater, thus suggesting that the urban PM2.5 samples have also a predominant marine influence. These findings are also in agreement with the mineralogical composition data, which shows the presence of gypsum with a clear marine origin on almost all samples, besides feldspar with an anthropogenic origin, and aluminosilicates from soil dust.