Spatiotemporal variability of submicrometer particle number size distributions in an air quality management district

Abstract

First measurements of ambient 10-1000 nm particle number concentrations (N-TOT) and size distributions were made at an urban, coastal, mountain and downwind site within the Central Taiwan Air Quality Management District during a cold and a warm period. The primary objectives were to characterize the spatial and temporal variability of the size-fractionated submicrometer particles and their relationships with copollutants and meteorological parameters. The results show that the ultrafine particles (< 100 nm) are the major contributor to the N-TOT. The mean N-TOT was highest at the urban site, whereas lower and comparable at the three other sites. Although the mean N-TOT at each site showed insignificant differences between study periods, their diurnal patterns and size distribution modal characteristics were modestly to substantially different between study sites. Correlation analyses of time-resolved collocated aerosol, copollutants and meteorological data suggest that the observed variability is largely attributable to the local traffic and to a lesser extent photochemistry and SO2 possibly from combustion sources or regional transport. Despite sharing a common traffic source, the ultrafine particles were poorly correlated with the accumulation particles (100-1000 nm), between which the latter showed strong positive correlation with the PM2.5 and PM10. Overall, the N-TOT and size distributions show modest spatial heterogeneity and strong diurnal variability. In addition, the ultrafine particles have variable sources or meteorology-dependent formation processes within the study area. The results imply that single-site measurements of PM2.5, PM10 or N-TOT alone and without discriminating particle sizes would be inadequate for exposure and impact assessment of submicrometer particle numbers in a region of diverse environments. (C) 2012 Elsevier B.V. All rights reserved.