title: Ultrafine particle size distributions near freeways: Effects of differing wind directions on exposure.
abstract: High ambient ultrafine particle (UFP) concentrations may play an important role in the adverse health effects associated with living near busy roadways. However, UFP size distributions change rapidly as vehicle emissions dilute and age. These size changes can influence UFP lung deposition rates and dose because deposition in the respiratory system is a strong function of particle size. Few studies to date have measured and characterized changes in near-road UFP size distributions in real-time, thus missing transient variations in size distribution due to short-term fluctuations in wind speed, direction, or particle dynamics. In this study we measured important wind direction effects on near-freeway UFP size distributions and gradients using a mobile platform with 5-s time resolution. Compared to more commonly measured perpendicular (downwind) conditions, parallel wind conditions appeared to promote formation of broader and larger size distributions of roughly one-half the particle concentration. Particles during more parallel wind conditions also changed less in size with downwind distance and the fraction of lung-deposited particle number was calculated to be 15% lower than for downwind conditions, giving a combined decrease of about 60%. In addition, a multivariate analysis of several variables found meteorology, particularly wind direction and temperature, to be important in predicting UFP concentrations within 150 m of a freeway (R2= 0.46,p= 0.014).
authors.affiliation: California Air Resources Board, Research Division, 1001 I Street, Sacramento, CA 95814, USA.
authors.forename: Kathleen H
authors.initials: KH
authors.lastname: Kozawa
authors.affiliation: Environmental Science and Engineering Program, Department of Environmental Health Sciences, School of Public Health, University of California, 650 Charles E. Young Drive South #46-081 CHS, Los Angeles, CA 90095-1772, USA.
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Winer
authors.affiliation: Preventive Medicine, Environmental Health Division, Keck School of Medicine, University of Southern California, 2001 North Soto Street, Los Angeles, CA 90089, USA.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Fruin
keywords: Freeways; Size distribution; Ultrafine particles; Wind direction