Short-Term Associations of Road Density and Road Features with In-Vehicle PM2.5 during Daily Trips in the Washington, D.C. Metro Area

Abstract

Increased daily exposure to fine particulate matter air pollution (PM2.5) is associated with increased morbidity, yet high exposures over shorter timeframes (e.g., hourly) may also play a role. Transportation is a milieu for increased transient pollution exposures. Both the road traveled and nearby roadways (i.e., surrounding road density) may play a role in increased PM2.5 exposure during commutes. For 2311 min of commutes, corresponding to 25 participants, we obtained in-vehicle PM2.5 exposures using personal monitors and, through GPS data, road features, including road density and road type (e.g., highway vs. local roads). We considered the density of both the surrounding highways and the local roads at 500 m and 1000 m resolutions. We estimated associations of road features with minute-averaged in-vehicle PM2.5 by applying linear mixed-effects models with random intercepts and autoregressive errors. The difference in log PM2.5, comparing the highest vs. lowest quartile of highway road density at 1 km resolution, was 0.09 log μg/m3 (95% confidence interval: 0, 0.19), which was similar to the difference between driving on highways vs. local roads (0.07 log μg/m3 (95% confidence interval: 0.00, 0.14)). Estimated differences were attenuated for local road density and 500 m resolution. The results were robust to adjustment for meteorology and ambient PM2.5. Unlike road features such as speed and road type, the surrounding road density is less modifiable during transportation. Therefore, road choice may not have a large impact on personal PM2.5 exposures.