PM2.5 and PM10 mass measurements in California's San Joaquin Valley

Abstract

PM2.5 and PM10 mass measurements from different sampling systems and locations within California's San Joaquin Valley (SJV) are compared to determine how well mass concentrations from a unified data set can be used to address issues such as compliance with particulate matter (PM) standards, temporal and spatial variations, and model predictions. Pairwise comparisons were conducted among 20 samplers, including four Federal Reference Method (FRM) units, battery-powered MiniVols, sequential filter samplers, dichotomous samplers, Micro-Orifice Uniform Deposit Impactors (MOUDIs), beta attenuation monitors (BAMs), tapered element oscillating microbalances (TEOMs), and nephelometers. The differences between FRM samplers were less than 10 and 20% for 70 and 92% of the pairwise comparisons, respectively. The TEOM, operating at 50 degrees C in this study, measured less than the other samplers, consistent with other comparisons in nitrate-rich atmospheres. PM2.5 mass measured continuously with the BAM was highly correlated with filter-based PM2.5 although the absolute bias was greater than 20% in 45% of the cases. Light scattering (B,p) was also highly correlated with filter-based PM2.5 at most sites, with mass scattering efficiencies varying by 10 and 20% for Bsp measured with Radiance Research nephelometers with and without PM2.5 size-selective inlets, respectively. Collocating continuous monitors with filter samplers was shown to be useful for evaluating short-term variability and identifying outliers in the filter-based measurements. Comparability among different PM samplers used in CRPAQS is sufficient to evaluate spatial gradients larger than about 15% when the data are pooled together for spatial and temporal analysis and comparison with models.