Inter- and Intra-Community Variability in Continuous Coarse Particulate Matter (PM10-2.5) Concentrations in the Los Angeles Area

Continuous coarse particulate matter (CPM, PM _10?2.5 ) concentrations were measured hourly at three different sites in the Los Angeles area from April 2008 through May 2009 as part of a larger study of the characteristics and toxicology of CPM. Mean hourly concentrations calculated seasonally ranged from less than 5 μg m ^–3 to near 70 μg m ^–3 at the three sites depending upon the CPM source variability and prevailing meteorology. Different diurnal concentration profiles were observed at each site. Correlation analysis indicates that CPM concentrations can generally be explained by wind-induced road dust re-suspension, particularly in drier seasons. CPM concentrations between the sites were not appreciably correlated and metrics used to assess variability between the sites—the coefficients of divergence—indicated that CPM concentrations were heterogeneous. The relative CPM contribution to observed PM ₁₀ concentrations varied by season and between sites. Additional concurrent CPM data available within a few km of the three sites indicate that intra-community variability can be on the same order as that observed for inter-community variability, although a similar analysis using PM ₁₀ data yielded reduced heterogeneity. The results indicate that accurate exposure assessment to CPM in the Los Angeles area requires measurements of CPM concentrations at different sites with higher temporal resolution than a single daily mean value.