Fine (1 ¿m) aerosol particles were collected at Alert, Canada (82¿27'N, 62¿30'W), during the Arctic spring as part of the Polar Sunrise Experiment 1997 and were analyzed for low molecular weight dicarboxylic acids (C2--C11) using gas chromatography with flame ionization detector (GC-FID) and GC/mass spectrometry (GC/MS). More than 80% of total diacids were detected in the fine fraction, suggesting the production by gas-to-particle conversion in the Arctic. In both fractions, oxalic acid was the dominant diacid species followed by succinic and malonic acids. Shorter chain diacids (C2--C5) showed the concentration maximum on 5--7 April; however, longer chain diacids (6) did not show a clear peak in the same periods. A significant depletion of ozone was observed during the experiment, where an anticorrelation was found between the concentrations of ozone and shorter chain diacids (C2--C5) in both fine and coarse aerosols. During this event, we also observed the enhanced concentration of filterable bromine in both modes. Peaks of dicarboxylic acids in both coarse and fine aerosols during ozone depletion events indicate that heterogeneous reactions are occurring on coarse particle and possibly on fine particles as well. Dicarboxylic acids may be produced by the oxidation of precursor compounds such as glyoxal and glyoxylic and other ω-oxocarboxylic acids that contain aldehyde (hydrated form) group, being involved with ozone and halogen chemistry in the Arctic marine boundary layer.