Characteristics of carbonate carbon in PM_2.5in a typical semi-arid area of Northeastern China

Daily concentrations of carbonate carbon (CC) in PM2.5collected in semi-arid area in Northeast China (Tongyu) were quantified by acidification that measures carbon dioxide (CO2) gas evolved using DRI Model 2001 Thermal Optical reflectance (TOR) Carbon Analyzer. The concentrations of CC during Asian dust storm (DS) and non-dust storm (NDS) periods during 14 April to 21 June, 2006 were determined and the transport pathways and possible sources for the CO32-aerosols were identified. Concentrations of CC in PM2.5collected from 14 April to 23 June, 2006 in Tongyu are ranged from 0.1 to 7.5μgCm-3with an average of 1.3μgCm-3. The average CC concentration during DS events was 2.6±1.7μgm-3, which was almost 4 times the daily average concentration of 0.6±0.5μgm-3during non-dust storm (NDS) period. Carbonate carbon accounted for 10% and 4% of total carbon in Tongyu during DS and NDS period, respectively. Carbonate concentrations were also derived by calculating the difference between cations and anions (ionic balance method). And good correlation is observed for the carbonate measured to the values for carbonate calculated from the ionic balance difference (R2=0.90). Higher correlations were observed between Ca with selected water-soluble ions (sulfate, nitrate or chloride) and elemental carbon in DS than in NDS periods. This is consistent with previous studies that more calcium salts (sulfate, nitrate or chloride) were formed during atmospheric transport during DS period. During the DS in spring 2006, three groups (A to C) of air mass trajectories were identified that passed over Tongyu. In general, when the air mass came from northwest, and south or southwest to Tongyu, high concentrations of carbonate were observed.