Abstract: The diurnal and nocturnal variations of low molecular weight dicarboxylic acids(C₂～C₁₀) in the fine atmospheric aerosols of Nanjing were monitored in the campus of Nanjing University in March 14th—19th,2002.The results showed that the diurnal mass concentration of total diacids（average,350 ng/m³） was lower than the nocturnal one（average,460 ng/m³）.Oxalic acid was the most abundant diacids,followed by succinic and malonic acid.These C₂～C⁴ diacids accounted for 89% of the total diacids.Based on the ratio of malonate to succinate（C³/C⁴ average,（1.00）） which is used to distinguish primary sources from secondary sources of these diacids,it could be found that secondary sources contribute more to the atmospheric dicarboxylic acids than primary ones.And the ratio of adipic acid to azelaic acid（C⁶/C⁹）,an indicator of source strength of anthropogenic and biogenic precursors to the aerosol diacids,is（0.88） on average,suggesting that biogenic organic matter was a significant contributor to the diacids in Nanjing air.