In order to understand and predict the role of organic particles in the atmosphere their deliquescence behavior must be understood. Using an optical microscope coupled to a flow cell, we investigated the deliquescence of malonic, succinic, glutaric, and adipic acid particles with sizes ranging from 2 to 40 μm. Deliquescence relative humidities were determined for temperatures ranging from 293 to 243 K. Over this temperature range both succinic acid and adipic acid deliquesced at approximately 100% relative humidity, whereas malonic acid and glutaric acid deliquesced at significantly lower relative humidities. These results are generally in good agreement with previous studies and are within 3% of calculations based on the UNIQUAC (universal quasi‐chemical) Functional Group Activity Coefficients (UNIFAC) model and recently published interaction parameters. Our studies also include measurements at temperatures below the eutectic temperatures. At these temperatures, ice did not nucleate; rather the particles underwent deliquescence to form metastable solution droplets. This indicates that solid dicarboxylic acids are not good ice nuclei above 243 K and hence will probably not play a role in ice cloud formation at these temperatures.