Increasing our understanding of aerosol properties is important because of their potential impacts on visibility, human health, and sensitive ecosystems. The Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study was conducted in 2006 to identify the sources, transport, and speciation of atmospheric gases and aerosols throughout Colorado that influence Rocky Mountain National Park (RMNP). As one component of this study, Micro-Orifice Uniform Deposition Impactor (MOUDI) samples were collected at two sites in the vicinity of RMNP. Samples were taken over a time span of 48 hours each during a period of 36 days in the spring (March-April) and summer (July-August). The samples were analyzed by ion chromatography to determine the concentrations of NH4+, Na+, Ca2+, K+, Mg2+, Cl-, NO2-, NO3-, SO42-, and C2O42- in either ten or twelve different size bins from >18 μm to <0.18 μm. The diameter of nitrate has important implications for nitrogen deposition in RMNP as larger particles have a higher deposition velocity. In the spring, nitrate was observed to be mainly in the accumulation mode while in the summer it was primarily in the coarse mode. Ammonium and sulfate were the dominant species in the accumulation mode and on several days the sulfate was sufficient to completely neutralize ammonium. However, there were a substantial number of days where the addition of nitrate and oxalate to the ammonium neutralization was not enough to account for complete neutralization. The excess ammonium suggests that other organic acids may be an important component of the aerosol in the region. There is a dearth of research on the size distribution and secondary formation pathways of organic acids, such as aerosol oxalate, which might be contributing to haze and acting as cloud condensation nuclei. The size distribution of oxalate was found to peak in the accumulation mode, specifically between 0.32 and 0.56 μm. We examined three potential contributors to oxalate concentrations: biomass burning, in-cloud processes, and gas-phase photo-oxidation. All three were found to be likely emission and formation mechanisms, but it is unclear which pathway is dominant.