In the spring nitrate was observed to be mainly in the accumulation mode while in the summer it was primarily in the coarse mode. The size of nitrate has important implications for nitrogen deposition in RMNP as larger particles have a higher deposition velocity. Ammonium and sulphate were the dominant species in the accumulation mode and on several days the sulphate was sufficient to fully neutralize ammonium. However, there were a significant number of days where the addition of nitrate and oxalate to the ammonium neutralization was not enough for full neutralization. The excess ammonium suggests other organic acids may be an important component of the aerosol in the region. There are few studies that have reported the size distribution of oxalate. The size distribution of oxalate was found to peak in the accumulation mode, specifically between 0.32 and 0.56 μm. While the majority of oxalate was observed in the accumulation mode some was also observed in the coarse mode. We examined the potential for oxalate formation via in-cloud and photo-oxidation processes but it is unclear which pathway is dominant without further measurements.