The Relationship Between PM2.5 and Altitude in Chicago During Spring 2023

In an urban area like Chicago, day-to-day life does not occur simply at ground level. Many residents and commuters live and work in high-rise buildings. We investigated how concentrations of fine particulate matter (PM_2.5) vary across building stories of different altitudes. PM_2.5 was measured using PurpleAir sensors, which provide live, publicly visible air quality data via a digital map. We installed outdoor PurpleAir sensors for a month on floors one, four, six, and nine of BVM Hall, an office building at the Lakeshore Campus of Loyola University Chicago. We also collected data for the same time period from a public PurpleAir sensor that was installed on the fourteenth floor of the Malibu Condominium a few blocks away. Our results show that as altitude increases, PM_2.5 concentration initially increases up to an altitude of roughly 14 meters and then decreases with altitude. This pattern is especially pronounced between midnight and eight AM, when cooler temperatures and a low planetary boundary layer create relatively stable atmospheric conditions. Overall these findings are consistent with past research indicating that air pollution concentrations will generally decrease with altitude, and our work will help inform short- and long-term decisions made by community members and policy makers regarding the exposure to air pollution by those living in urban areas.