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

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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 (CO 3 2− ) fraction was determined by sample acidification and thermal evolution. The CO 3 2− accounted for 8.0 ± 0.8% of particles with aerodynamic diameter ≤2.5 μm (PM 2.5 ) during dust storms and 4.7 ± 3.0% of PM 2.5 between storms. The ratios of calcium to carbonate carbon were consistent with those of calcite (CaCO 3 ). The δ 13 C and δ 18 O abundances in dust storm samples were −2.7 ± 0.7‰ and −5.8 ± 1.5‰, which differed from −8.3 ± 1.9‰ for δ 13 C and −10.8 ± 2.0‰ for δ 18 O during normal conditions. The δ 13 C is positively correlated with δ 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 CO 3 2− (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.