Urban Spatial Monitoring of Pollutants Using Light Rail-Based Sensor Systems

High wintertime particulate and summertime ozone pollution episodes occur annually within the urbanized Salt Lake Valley in Utah, and can factor into health, economic, and other impacts to residents. The spatial and temporal distributions of these episodes can vary greatly due to topographic and meteorological factors such as local terrain flows, Great Salt Lake breezes, boundary layer structure, etc. To begin to better assess these spatial distributions, a pilot project was started several years ago to install sensor packages containing fine particulate matter and ozone sensors on top of two electric light rail vehicles operating routinely within the greater Salt Lake Valley.

Starting in late 2018, the pilot project was moved into an operational phase, with upgrades to sensor equipment, maintenance, communication, and data archival protocols. Sensor packages on two separate light rail cars collect and locally store pollutant (PM2.5 and ozone) measurements every 2 seconds as they traverse multiple commuter rail lines in the Salt Lake Valley. A third train will also be installed to expand the coverage to the entire light-rail network and encompass the majority of the ~1 million population in Salt Lake county. These observations are transmitted into a provisional archive system and made available through a variety of web-accessible resources. Additionally, two fixed-site particulate monitors were installed to help provide validation of the mobile-based sensors relative to official measurements taken by the Utah Division of Air Quality. A description of the sensor packages deployed, ongoing validation and data quality control efforts, and case examples during high-impact air quality episodes are provided.