Confronting Uncertainties of Simulated Air Pollution Concentrations during Persistent Cold Air Pool Events in the Salt Lake Valley, Utah

Abstract

Air pollutant accumulations during wintertime persistent cold air pool (PCAP) events in mountain valleys are of great concern for public health worldwide. Uncertainties associated with the simulated meteorology under stable conditions over complex terrain hinder realistic simulations of air quality using chemical transport models. We use the Community Multiscale Air Quality (CMAQ) model to simulate the gaseous and particulate species for 1 month in January 2011 during the Persistent Cold Air Pool Study (PCAPS) in the Salt Lake Valley (SLV), Utah (USA). Results indicate that the temporal variability associated with the elevated NOx and PM2.5 concentrations during PCAP events was captured by the model (r = 0.20 for NOx and r = 0.49 for PM2.5). However, concentrations were not at the correct magnitude (NMB = −35/12% for PM2.5 during PCAPs/non-PCAPs), where PM2.5 was underestimated during PCAP events and overestimated during non-PCAP periods. The underestimated PCAP strength is represented by valley heat deficit, which contributed to the underestimated PM2.5 concentrations compared with observations due to the model simulating more vertical mixing and less stable stratification than what was observed. Based on the observations, the dominant PM2.5 species were ammonium and nitrate. We provide a discussion that aims to investigate the emissions and chemistry model uncertainties using the nitrogen ratio method and the thermodynamic ammonium nitrate regime method.

Source–Receptor Relationships Between Precursor Emissions and O3 and PM2.5 Air Pollution Impacts

“…PCAPS captured PM 2.5 nitrate ion regional gradients as the model predicted the highest levels in the upper midwest, which is consistent with ambient measurements. The model underpredicted PM 2.5 nitrate ion in areas of the western U.S. known for complex topography, emissions, and meteorology that can result in periods of high wintertime levels. , The PCAPS correlation to ambient measurements was better for PM 2.5 sulfate ion and elemental carbon than other reduced complexity tools and comparable to those same tools for PM 2.5 nitrate ion (Figure ). PCAPS also compared similarly to the performance of other reduced complexity tools when considering fractional bias and fractional error metrics (Figure ).…”

Effects of Secondary Organic Aerosol Water on fine PM levels and composition over US

“…Aerosol liquid water directly affects the PM sensitivity and dry deposition rates, with direct implications for emissions control policy (Nenes et al, 2020;Nenes et al, 2021;Sun et al, 2021). Given this, and the important role of SOAW for climate forcing, visibility and chemistry, its inclusion in future studies is highly recommended.…”