Data from: Yellow Air Day Advisory Study

Using a dataset consisting of daily vehicle trips, PM2.5 concentrations, along with a host of climactic control variables, we test the hypothesis that “yellow air day” advisories provided by the Utah Division of Air Quality resulted in subsequent reductions in vehicle trips taken during northern Utah’s winter-inversion seasons in the early 2000s. Winter inversions occur in northern Utah when climactic conditions are such that PM2.5 concentrations (derived mainly from vehicle emissions) become trapped in the lower atmosphere, leading to unhealthy air quality (concentrations of at least 35 µg/m3) over a span of what are called “red air days”. When concentrations rise to between 15 and 25 µg/m3 on their way to the 35 µg/m3 threshold, the region’s residents are informed via several different media sources and road signage that the region is experiencing a yellow air day, and urged to reduce their vehicle usage during the day. Our results suggest that yellow air day advisories have been at best weak, at worst perverse, measures for reducing vehicle usage on yellow air days and ultimately for mitigating the occurrence of red air day episodes during northern Utah’s winter inversion season.