Moss bag biomonitoring of airborne elements at a suburban background site in Belgrade (Serbia) during Saharan dust intrusions
(1) Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia, (2) University of Belgrade, Faculty of Chemistry, Studentski trg 12 – 16, 11000 Belgrade, Serbia, (3) Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Joliot Curie 6, 141980 Dubna, Russian Federation
During the spring/summer season 2019, characterized by several Saharan dust episodes, two moss species, Hypnum cupressiforme and Sphagnum girgensohnii, were exposed for twelve consecutive periods of 15-days, and also for one-, two-, three-, four-, five- and six months. In addition, particulate matter (PM10 and PM2.5) was sampled during and after the identified dust episodes. As an estimate of the dust amount to which the moss bags were exposed during 15-day periods, we used MERRA-2 (The Modern-Era Retrospective analysis for Research and Applications) predictions of dust concentrations at ground level, averaged over these periods. The concentrations of Al, Ba, Ca, Fe, K, Mg, Mn, P, S, Sr, Zn, Ni, V, Cr, Co, Cu, As, Cd, Pb, Ga, Y, and Tb were measured in the moss and PM samples. The results showed that 15-day bag exposure at the background location could not provide a valuable ʻsignalʼ of the elements in the moss transplants, except for Al, V, As, Ga, Y, and Tb. Extended moss bag exposure of a couple of months provided a stabile enrichment of the majority of the elements in the mosses. An increase of the PM mass concentrations, but still below the daily threshold values, was measured at the studied site during two of three recorded Saharan dust intrusions. In the PM10 samples the concentrations of Al, V, Ga, Y, and Tb were increased multifold during one of the episodes that was particularly intense. The same elements in the S. girgensohnii moss bags, consecutively exposed for 15-day periods in the season, showed a slight increase of the concentrations that overlapped with these episodes. The ratio of crustal elements (Ca/Al and Mg/Al) in PM10 (dust days) and moss samples (3-month exposed) were in line of those reported for dust transported from western Africa. The As/Al ratio in PM10 and moss samples corresponding to dust episodes were smaller than those for non-dust days/periods, which could be used to distinguish natural (dust) from anthropogenic pollution.
Keywords: Air Pollution; Element Content; Active Moss Biomonitoring; Bag Exposure Period; Saharan Dust Intrusion
