Size-segregated atmospheric aerosols (11 stages separating particles from <0.04 to >14.2 μm) collected in the Arctic during the polar sunrise at Alert were analyzed for aerosol mass, dicarboxylic acids, and major inorganic ions. Oxalic, malonic, succinic, and glutaric acids were detected in all size ranges, with oxalic acid being dominant. Their concentrations maximized in the accumulation mode either at 0.24–0.40 or 0.40–0.8 μm aerodynamic diameters, suggesting that diacids were mainly formed by gas-to-particle conversion via photochemical oxidation of nonmethane hydrocarbons and oxygenated organics originated from continental pollution sources. The relative abundances of oxalic acid were higher in the 0.24- to 0.4-μm size particles (73–78%) than in supermicrometer particles (40–60%), indicating that oxalic acid is produced by gas phase oxidation of precursors followed by accumulation on preexisting particles. Mass size distributions of NH4+ and SO42− peaked in the accumulation mode similar to those of small diacids. The sea-salt enrichment factor of K+ (biomass burning tracer) relative to Na+ maximized in 0.1- to 0.8-μm sizes, whereas those of Mg2+ and Ca2+ (dust tracers) in 0.4- to 7.8-μm particles. Maximized chlorine loss and bromine enrichment were found at 0.4–0.8 and 0.24–0.4 μm sizes, respectively. Concentrations of Br−, which typically showed a submicrometer maximum, increased significantly during an O3 depletion event having a shift of size distribution to a supermicrometer mode. During this event, oxalic acid concentration relative to succinic acid increased in submicrometer mode (0.24–0.4 μm), adding to a growing body of evidence supporting the hypothesis that halogen chemistry is important in the production and loss of oxalic acid in the arctic atmosphere.