The role of large particles in aerosol concentration and flux estimates; a comparison of Total Suspended Particulate, PM10 and PM2.5 measurements for use in biogeochemical studies

The composition of atmospheric aerosols are a diverse and common feature in urban and rural environments. The majority of the existing aerosol monitoring networks focus on the small particle size classes of less than 2.5 and 10 μm. These size classes are a focus in federal environmental law and have a major potential impact on human health. These particle classes are not the only particles in the atmosphere and particles > 10 μm can be a significant component of the atmospheric aerosol load and biochemical inputs to ecosystems. For estimates of elemental flux or mass transport through the atmosphere, these large suspended particulates can represent an important flux that may not be captured in existing observational networks. In this study, we compare PM 2.5, 10 and Total Suspended Particulate (TSP) concentrations and estimate fluxes for several different instruments during a simultaneous deployment near Boulder, Colorado. In this site, the contribution of > 10 μm particles to total concentrations varied during the three month sampling period. In some instances TSP concentrations may have exceeded the 10 μm particle concentrations by 300 percent while at other times the particles present were mainly in the sub 10 μm size classes. Some of the variation in particle size classes appears related to variability in the contribution of industrial, biological and mineral aerosols to the total atmospheric load as well as the ability of local to regional transport by winds. For element flux estimates, and particularly for some major, and biogeochemically relevant elements such as P and N, we suggest that the large particles embedded in the TSP category of aerosols may represent a biologically significant flux of material to ecosystems.