Magnetic properties of daily sampled total suspended particulates in Shanghai

Samples of total suspended particulates (TSPs) and <10 mu m fractions (PM10) collected daily from in and around two industrial districts in Shanghai, China, during November 1998 have been examined using environmental magnetic measurements. Statistical classifications of the data show that the 11 sampling sites can be classified into four categories of magnetic properties, each expressing a different combination of mainly local dust sources, Changes in meteorological conditions, particularly wind direction, cause daily shifts in particulate types and sources. Interpretation of the magnetic parameters suggests roughly constant proportions of high coercivity ("hematite") and low coercivity ("magnetite") mineral phases with a predominance of ferrimagnetic grains in superparamagnetic (SP) and multidomain (MD)+ pseudo single domain (PSD) sizes. Negative linear correlations between TSP concentrations and ferrimagnetic concentration parameters suggest that the dominant source of TSPs is weakly magnetic. Mass specific susceptibility (chi(LF)), saturation isothermal remanence (SIRM), susceptibility of anhysteretic remanent magnetization (chi(ARM)), and high field remanence magnetization (HIRM) appear to discriminate the different dusts from a range of sources, including iron and steel manufacturing, coal-fired combustion, construction industries and wind-blown soil. Measurements on samples from modern chimney stacks suggest that magnetic phases from coal-fired combustion processes are dominantly carried in <10 mu m particle fractions. Strongly ferrimagnetic particles in TSPs are probably linked more to combustion products from older technologies. PM10 samples appear to originate from a wide range of sources including combustion products and construction materials. Given previously reported links between magnetic properties and mutagenicity in respirable particulates, the results may help to identify areas of high health risk. The results demonstrate that magnetic measurements provide an exceptionally simple and effective approach for identifying daily variations in particulate loadings and sources in this urban environment.