Evaluation and optimization of an urban PM2.5 monitoring network

Abstract

The objective of this study was to evaluate the PM_2.5 monitoring network established in the Greater Cincinnati and Northern Kentucky metropolitan area for measuring the 24 h integrated PM_2.5 concentration, as well as—at selected sites—hourly PM_2.5 concentration and 24 h integrated PM_2.5 speciation. The data collected during three years at 13 measurement sites were analyzed for spatial and temporal variations. It was found that both daily and hourly concentrations of PM_2.5 have low spatial variation due to a regional influence of secondary ammonium sulfate. In contrast, the trace element concentrations had high spatial variation. Seasonal variation accounted for most of the total temporal variation (60%), while yearly, monthly, weekly and daily variations were lower. The variance components and cluster analyses were applied to optimize the number of sites for measuring the 24 h PM_2.5 concentration. It was found that the 13-site network may be optimized by reducing the number of sites to 8, which would result in a relative precision reduction of 9% and a relative cost reduction of 36%. At the same time, the data suggest that the spatial resolution of speciation monitors and real-time PM_2.5 mass monitors should be increased to better represent spatial and temporal variations of the markers of local air pollution sources.