Local and non-local sources of airborne particulate pollution at Beijing

A new element tracer technique has firstly been established to estimate the contributions of mineral aerosols from both inside and outside Beijing. The ratio of Mg/Al in aerosol is a feasible element tracer to distinguish between the sources of inside and outside Beijing. Mineral aerosol, inorganic pollution aerosol mainly as sulfate and nitrate, and organic aerosol are the major components of airborne particulates in Beijing, of which mineral aerosol accounted for 32%-67% of total suspended particles (TSP), 10%-70% of fine particles (PM(2.5)), and as high as 74% and 90% of TSP and PM2.5, respectively, in dust storm. The sources from outside Beijing contributed 62% (38%-86%) of the total mineral aerosols in TSP, 69% (52%-90%) in PM(10), and 76% (59%-93%) in PM2.5 in spring, and 69% (52%-83%), 79% (52%-93%), and 45% (7%-79%) in TSP, PM(10), and PM(2.5), respectively, in winter, while only similar to 20% in summer and autumn. The sources from outside Beijing contributed as high as 97% during dust storm and were the dominant source of airborne particulates in Beijing. The contributions from outside Beijing in spring and winter are higher than those in summer, indicating clearly that it was related to the various meteorological factors.