Characterization of airborne carbonate over a site near Asian dust source regions during spring 2002 and its climatic and environmental significance

[1] During spring 2002, three dust storm events were monitored by filter sampling in Xi'an near an Asian dust source region of northwest China. The carbonate (CO32-) fraction was determined by sample acidification and thermal evolution. The CO32- accounted for 8.0 +/- 0.8% of particles with aerodynamic diameter less than or equal to2.5 mm (PM2.5) during dust storms and 4.7 +/- 3.0% of PM2.5 between storms. The ratios of calcium to carbonate carbon were consistent with those of calcite (CaCO3). The delta(13)C and delta(18)O abundances in dust storm samples were -2.7 +/- 0.7parts per thousand and -5.8 +/- 1.5parts per thousand, which differed from -8.3 +/- 1.9parts per thousand for delta(13)C and -10.8 +/- 2.0parts per thousand for delta(18)O during normal conditions. The delta(13)C is positively correlated with delta(18)O values (r = 0.78). This first measurement of isotopic abundance in Asian dust indicates the potential to quantify its contribution at distant locations using receptor models. By increasing the alkalinity of ocean water in the Pacific Ocean and buffering the atmospheric acidity of east Asia, the large amounts of airborne CO32- ( as high as 44.8 Tg yr(-1)) entrained by Asian dust may provide an important atmospheric alkaline carbon reservoir for large-scale climatic and environmental changes.