Wintertime PM2.5 concentrations during persistent, multi-day cold-air pools in a mountain valley

► Series of persistent cold-air pools (CAP) formed in Salt Lake Valley 1 Jan - 20 Feb 2011. ► PM2.5 concentrations increased with time and CAP strength. ► Within CAPs, ground-level PM2.5 concentrations decreased with altitude. ► During 23-30 Jan CAP, rate of increase in PM2.5 concentration was linear at 6 μg (m3 day)−1. ► Breakup of CAP on 16 Jan 2011 occurred first at higher elevations.