Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/8007
AuthorsSagnotti, L.* 
Winkler, A.* 
TitleOn the magnetic characterization and quantification of the superparamagnetic fraction of traffic-related urban airborne PM in Rome, Italy
Issue DateNov-2012
Series/Report no./59 (2012)
DOI10.1016/j.atmosenv.2012.04.058
URIhttp://hdl.handle.net/2122/8007
KeywordsParticulate Matter
Air pollution
Environmental magnetism
Superparamagnetic particles
Hysteresis properties
Subject Classification04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism 
AbstractThe magnetic properties of traffic-related airborne particulate matter (PM) in the city of Rome, Italy, have been previously analyzed and interpreted as suitable proxies to discriminate between different vehicular sources. In this study, we carried out a new set of measurements and analyses specifically devoted to the identification and evaluation of the contribution of ultrafine superparamagnetic (SP) particles to the overall magnetic assemblage of traffic-related PM in Rome. In particular, the presence and the concentration of SP particles have been estimated on powders collected from disk brakes and gasoline exhaust pipes of circulating vehicles and from Quercus ilex leaves grown along high-traffic roads, measuring their hysteresis parameters in a range of temperatures from 293 K to 10 K and measuring the time decay of their saturation remanent magnetization (MRS) at room temperature. The SP fraction contributes for the 10-15% to the overall room temperature MRS and causes the observed changes in the hysteresis properties measured upon cooling down to 10 K. In all the analyzed samples the SP fraction is associated to a generally prevailing population of larger ferrimagnetic multidomain (MD) particles and we suppose that in traffic-related PM the SP fraction mainly occurs as coating of MD particles and originated by localized stress in the oxidized outer shell surrounding the unoxidized core of magnetite-like grains. Under this hypothesis, the estimate of SP content in traffic-related PM cannot be considered a robust proxy to estimate the overall concentration of nanometric particles.
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