Monday, 15 January 2007: 11:15 AM
Size Distribution and Hygroscopic Properties of Agricultural Aerosols
212A (Henry B. Gonzalez Convention Center)
Due to significant atmospheric loadings of agricultural dust aerosols, they must be considered in assessments of the impacts of aerosols on visibility, climate forcings and human health. A GRIMM aerosol spectrometer and Sequential Mobility Particle Sizer and Counter (SMPS) measurements were simultaneously performed during a recent campaign at a feedlot in the Texas Panhandle to characterize the size distribution of agricultural aerosols as a function of time in an overall size range of 11 nm to 20 Ám diameters. To explore the hygroscopic nature of agricultural particles, size-resolved aerosol samples were collected using a cascade impactor system at the feedlot, and hygroscopicity measurements were conducted on these samples using an Environmental Scanning Electron Microscope (ESEM) at our laboratory. The elemental compositions of the particles were also determined using an Energy Dispersive X-ray Spectroscope (EDS). Our results indicate that majority of agricultural particles do not take up significant amounts of water when exposed to relative humidities (RH) up to 93.94%. A notable exception to this is that a fraction of the coarse mode particle population deliquesced at approximately 75% RH and grew to twice their original dry sizes at an RH of 93.94%. Ultimately, this study may improve our understanding of how the hygroscopic, chemical and morphological properties of agricultural particles influence climate and air quality at a regional to global level.