[Magnetic response of street tree leaves to particulate pollution in Shanghai]

To reveal the magnetic response to atmospheric particulate pollution in tree leaves along urban streets, twenty-four evergreen tree leaves were collected from green belt along Jinshajiang road, Shanghai, which were subjected to magnetic and heavy metals (Zn, Cu, Pb) analyses. The result revealed that in all leaf samples chi, SIRM varied in ranges of (4-59) x 10(-8) m3 x kg(-1) and (496-6 114) x 10(-6) Am2 x kg(-1), respectively, S(-300mT) varied from 89% to 98% and chi(ARM)/chi < 4, chi(ARM)/SIRM < 30 x 10(-5) mA(-1) was found. The magnetic parameters showed that ferromagnetic/ferrimagnetic particles were the main magnetic carriers in dust-loaded tree leaves, and magnetic grains were predominantly pseudo-single domain (PSD) and multidomain (MD) in size. The significant positive correlation between heavy metals (Zn, Cu, Pb) contents and chi, SIRM, chi(ARM), suggested that magnetic parameters like SIRM could be used as a proxy for heavy metal contents. We recommend that Magnolia grandiflora, widely distributed in Shanghai, can be used for particulate pollution monitoring.