1193215 - Black Carbon Exposures and Trends in Detroit, Michigan: Synthesis of Fixed, Mobile, and Indoor 2019-2020 Measurements

Black carbon (BC) is a component of fine particulate matter (PM2.5) with strong light-absorbing properties, climate warming potential, adverse impacts on human health, and a high correlation with traffic emissions in urban areas, especially emissions from heavy-duty diesel trucks. This study conducted an integrative analysis examining spatial and temporal trends and long-term BC exposures in southwest Detroit, which is home to vulnerable communities as well as extensive truck traffic and industrial emissions. The area is unusual in the density and nature of ambient and indoor monitoring, and the extensive truck traffic on both highways and many surface streets. We analyze three datasets. First, six fixed sites have continuously monitored hourly BC concentrations (and other pollutants) since late 2018. Second, 5-minute BC concentrations have been measured across the region using a mobile platform, the Michigan Pollution Assessment Laboratory (MPAL), on about two days per week. Third, 15-minute BC measurements have been obtained inside and outside of 37 residences, all located within 65 to 900 m of a major interstate highway. These data show striking spatial patterns, with southwest Detroit experiencing BC levels approximately twice those found elsewhere, but nearby, in the urban area. Time-of-day and day-of-week patterns are correlated to traffic flows, also implicating truck traffic. Data acquired by the mobile platform, providing high-resolution spatial information, illustrate high levels along trucking routes and gradients that reflect dispersion from sources, supplementing the patterns illustrated by the continuous fixed-site monitoring. The indoor measurements show high BC levels in most homes, and that indoor and outdoor levels are very similar, indicating high penetration of BC indoors, little filtration or attenuation of BC indoors, and the significance of exposure to residents. Trends of BC levels show effects of the March to April 2020 COVID-19 “lockdown,” but levels have climbed upwards. Importantly, BC trends differ significantly from PM2.5. Overall, these data suggest that local diesel exhaust emissions is a major source of BC and PM2.5 in the region, and that exposures and health risks can be lowered by reducing and rerouting truck traffic, improving emission controls, and using buffers and filters to reduce indoor levels.