Atmospheric pollution assessed by in situ measurement of magnetic susceptibility on lichens

Abstract

The use of environmental magnetism methods and biomonitors allows us the development of a low-cost tool for assessing atmospheric pollution through trapped magnetic particulate matter. Such particles concentration was monitored in situ, on the lichen's thallus, using magnetic susceptibility as a pollution proxy. We studied the magnetic particle distribution on the thallus surface from weekly measurements of in situ magnetic susceptibility κis during 16 months for seven sites. A total of ∼8300 measurements was carried out; and mean overall κis values for each lichen varied between 4.1 and 23.9 × 10−5SI revealing the influence of different atmospheric pollution sources on Parmotrema pilosum, such as metallurgical factories and vehicular emissions. Weekly measurements of κis show areas of magnetic accumulation on the thallus over a period of 60 measurement campaigns. Iron rich spherules and irregular particulate matter between PM2.5 and PM1.0 were observed by SEM-EDS. A joint analysis of meteorological variables and magnetic susceptibility shows an inverse relation between this magnetic parameter and temperature, i.e., a trend of decreasing κis values during seasons of higher temperatures which tend toward higher values of atmospheric mixing height. Precipitation also affects the magnetic signal over time, producing decreases in mean values of κis after rainy periods.