Atmospheric particle deposition on mesquite leaves in the central Arizona-Phoenix area

One technique that has been used to analyze individual atmospheric particles is automated electron microscopy. This technique gives the size, shape, and elemental composition of individual particles and has been used successfully for particles collected on filters in particle samplers. The goal of the current project is to mimic this electron microscopy analysis technique for particles deposited on leaf surfaces. Preliminary results demonstrate that electron microscopy can be used successfully to analyze individual particles on leaf surfaces. The ability to analyze atmospheric particles on leaf surfaces leads to a specific application: determining the spatial distribution of atmospheric particles throughout urban areas, namely Phoenix. Evidence from past studies in Phoenix indicate that the distribution of particle types is non-uniform, and sampling with a limited number of particle samplers is not adequate for capturing this variability. Using leaves gives the ability to sample in more locations. In a preliminary study, three sampling locations from the Phoenix area - a desert, an urban, and a suburban site - were chosen as test sites to determine whether different particle types could be observed on leaf surfaces from the different sites. The particle types from the desert site contain only elements comprising desert dust. The particle types from the urban and suburban sites consist partially of elements found in desert dust, but they also contain sulfur, which is likely from anthropogenic sources within the urban area. These preliminary results indicate that the distribution of particle types throughout an urban area can be determined from the analysis of particles on leaf surfaces. A more detailed study is in progress. Leaves from twenty-eight sampling sites around the Phoenix area have been collected and will be analyzed with a method similar to that used in the preliminary study. The twenty-eight sites were chosen based on land-use data. In addition to determining the spatial distribution of particle types, another objective of this work correlate the particle types with the land-use data from which they were collected.