Salt Lake City (SLC) frequently experiences severe wintertime pollution due to the accumulation of fine particulate matter, which is dominated by ammonium nitrate (AN) during atmospheric inversion events. Recent measurements in SLC have shown that heterogeneous reactions between gaseous dinitrogen pentoxide (N₂O₅) and ambient aerosol drives AN accumulation in SLC. However, information is lacking on the ambient aerosol sources present, and how efficiently these particles react with N₂O₅ to form AN. As such, we deployed an ambient aerosol flow tube coupled to a chemical ionization mass spectrometer and particle sizing instrumentation at the University of Utah in winter to probe the reactive uptake of N₂O₅ (γN₂O₅)that leads to AN formation. Aerosol particle composition was measured from offline filter collections and ion chromatography to determine how different particle sources react with N₂O₅. Under inversion conditions, we measured suppressed values of γN₂O₅ (median γN₂O₅ = 0.03 ± 0.04) that decreased to as low as 0.001 when high AN was measured, suggesting that the nitrate effect suppresses γN₂O₅ by ~ 0.02 per night. Under clean conditions, we observed elevated values of γN₂O₅ (median γN₂O₅ = 0.06 ± 0.05) due to efficient heterogeneous reactions with mineral dust, ammonium sulfate, and road salt aerosol with no notable decrease in γN₂O₅ throughout clean periods. Using a 1-dimensional chemical box model, we find that aerosol nitrate accumulation is limited when γN₂O₅ is less than 0.01 throughout the evening. These results suggest that the most important influence on γN₂O₅ in wintertime SLC is the nitrate effect.