Spatial variation of resuspended particulate matter in urban environments and real-world assessment of street sweeping

Non-tailpipe emissions have gained growing attention as an emerging source of traffic-related air pollution, especially as tailpipe emissions decline. This study conducted extensive mobile measurements in a high-density urban area over two years to investigate the spatial variability of resuspended road dust and evaluate the real-world effectiveness of street sweeping. Resuspended particulate matter (PM), specifically PM_2.5 and PM₁₀, was measured alongside pollutants from tailpipe and non-tailpipe sources. The mobile sampling revealed substantial spatial variability in resuspended PM with notably higher concentrations on local streets compared to major roads. This spatial pattern contrasted with tailpipe-related black carbon and ultrafine particles, which were elevated near highways, commercial, and industrial zones. Nearby construction and renovation activities were major contributors to resuspended PM on local streets. As a result, school neighborhoods in residential areas and open spaces may experience acute exposure to road dust PM. Street sweepers equipped with regenerative air systems were generally ineffective in reducing resuspended PM under real-world conditions. This trend was consistent across different types of regenerative sweepers and operational modes, except for one sweeper equipped with an advanced filtration system showing some reduction in resuspended PM. Operational factors, including sweeper speed and water spraying, substantially influenced PM resuspension. While water spraying reduced on-road PM during sweeping, excessive use resulted in unintended increases in both resuspended and on-road PM concentrations afterward. While street sweeping helps to manage debris on road surfaces, these findings underscore the need to optimize sweeping practices and develop strategies to improve near-road air quality.