Urban-Scale Seasonal and Spatial Variability of Ultrafine Particle Number Concentrations

In epidemiological studies, ultrafine particle (UFP) data from a single monitoring site are generally used as a measure of population exposure potentially resulting in exposure misclassification. From August 2009 to October 2010, 1-week campaigns were conducted during each season. The temporal and spatial variations of UFP number size distributions were investigated at 12 monitoring sites distributed across a 9 × 9 km urban area in Rochester, New York using a Fast Mobility Particle SizerTM spectrometer. The overall average number concentrations of 5.6- to 560-nm particles in summer, winter, spring, and fall were 9,025, 10,939, 4,955, and 14,485 cm−3, respectively. Coefficients of divergence and correlation coefficients were calculated between site pairs to assess the spatial heterogeneity in the particle number size distributions. Moderate spatial divergence and uniform temporal variation were found for the chosen sites. Elevated UFP number concentrations were observed near highways, off-road diesel engines, and residential wood combustion sources, indicating significant contributions to the UFP exposure of people living adjacent to these sources. Our results suggest that one stationary monitoring site may not represent the actual human UFP exposure over a whole urban area.