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

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 ≤2.5 μm (PM2.5) during dust storms and 4.7 ± 3.0% of PM2.5between storms. The ratios of calcium to carbonate carbon were consistent with those of calcite (CaCO3). The δ13C and δ18O abundances in dust storm samples were -2.7 ± 0.7‰ and -5.8 ± 1.5‰, which differed from -8.3 ± 1.9‰ for δ13C and -10.8 ± 2.0‰ for δ18O during normal conditions. The δ13C is positively correlated with δ18O 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.