UCLA

As car manufacturers have reduced vehicle tailpipe emissions, roadway sources of PM2.5 (particulate matter with diameters ≤ 2.5 μm) generated by brake wear, tire wear, and resuspended dust from the roadway have played an increasingly significant role in near-roadway exposure. In this study we used the spatially dense network of low-cost PurpleAir (PA) sensors. Approximately 400 sensors are deployed in Los Angeles County, with 22 located within 700 meters of a major roadway. Plotting the PM2.5 concentrations for each PA sensor located within 700 meters of a roadway between January 2019 and December 2021 revealed no distance-decay trend. We then used the nearby personal weather stations to determine the hourly wind direction at each sensor and separated PM values according to whether they were downwind or upwind of their respective nearby roadways. The results showed that fine particles (PM2.5) were elevated within 240 meters of the roadway and decayed to the background concentration by 430 meters. The concentrations were 16 to 24% higher than the background concentration and were higher in periods of higher atmospheric stability and lower wind speeds.