Residential exposure to local traffic emissions associated with higher risk of stroke

By Yicong Yang

A recent study finds that long-term residential exposure to locally emitted black carbon (BC)—primarily from traffic exhaust—is associated with higher stroke incidence. BC comprises a significant portion of particulate matter. Although BC is a known health hazard with health effects that are especially pronounced in populations in dense urban areas, the U.S. does not currently include it as a separate criteria pollutant in its National Ambient Air Quality Standards.

A group of researchers calculated source components of particulate matter (PM10 and PM2.5) and black carbon (BC) in Gothenburg, Stockholm, and Umeå, three Swedish cities with low levels of overall air pollution. The source components include residential heating, road wear, traffic exhaust, industry, shipping, and other sources. Researchers then used statistical models to investigate how these source components are associated with Ischemic Heart Disease (IHD) or stroke incidence retrieved from hospital registry data. For every 0.31 µg/m3 additional exposure to locally emitted BC, the risk of hospitalization or mortality from stroke in the same year is estimated to be increased by 4.1 percent. Two other air pollutants – PM10 and PM2.5 – were not associated with stroke.

Black carbon is the sooty black material emitted from gas and diesel engines, coal-fired power plants, and other sources that burn fossil fuel. BC has negative effects on human health and global climate. In this research, traffic exhaust was the largest local contributor to BC in urban neighborhoods as compared to residential heating and other sources.

In the United States, much attention has been paid to PM2.5 from motor emissions. The Congestion Mitigation and Air Quality Improvement Program makes funds available to state and local governments for transportation projects that will help them meet the requirements of the Clean Air Act. Effective approaches include vehicle improvement and emission control technologies. However, there is no specific criteria for black carbon pollution. BC levels tend to be high on congested urban street and road segments, with a particularly negative health effect on populations using the road or living, working, and shopping nearby. This research points to the need to address localized pollution that is currently not being tracked.

Yicong Yang is a Project Assistant at SSTI.