Donald M. Hooper

Measurement of airborne particle concentrations near the Sunset Crater volcano, Arizona.

Direct measurements of airborne particle mass concentrations or mass loads are often used to estimate health effects from the inhalation of resuspended contaminated soil. Airborne particle mass concentrations were measured using a personal sampler under a variety of surface-disturbing activities within different depositional environments at both volcanic and nonvolcanic sites near the Sunset Crater volcano in northern Arizona. Focused field investigations were performed at this analog site to improve the understanding of natural and human-induced processes at Yucca Mountain, Nevada. The level of surface-disturbing activity was found to be the most influential factor affecting the measured airborne particle concentrations, which increased over three orders of magnitude relative to ambient conditions. As the surface-disturbing activity level increased, the particle size distribution and the majority of airborne particle mass shifted from particles with aerodynamic diameters less than 10 &mgr;m (0.00039 in) to particles with aerodynamic diameters greater than 10 &mgr;m (0.00039 in). Under ambient conditions, above average wind speeds tended to increase airborne particle concentrations. In contrast, stronger winds tended to decrease airborne particle concentrations in the breathing zone during light and heavy surface-disturbing conditions. A slight increase in the average airborne particle concentration during ambient conditions was found above older nonvolcanic deposits, which tended to be finer grained than the Sunset Crater tephra deposits. An increased airborne particle concentration was realized when walking on an extremely fine-grained deposit, but the sensitivity of airborne particle concentrations to the resuspendible fraction of near-surface grain mass was not conclusive in the field setting when human activities disturbed the bulk of near-surface material. Although the limited sample size precluded detailed statistical analysis, the differences in airborne particle concentration over 900-y weathered volcanic and nonvolcanic deposits appeared to be potentially significant only under heavy surface disturbances.

A new methodology to monitor soil moisture over a complex arctic environment, Kobuk River valley, Alaska

Frozen ground is a sensitive indicator of environmental change. In this study, we examine the relevance of L-band synthetic aperture radar (SAR) data for extracting information on frozen ground, above discontinuous permafrost, in the Kobuk River valley, Alaska. A new methodology based on multi-temporal image acquisition is presented. This approach uses Ohs model with image acquisition during the period of frozen ground, and incorporates a vegetation model during the thawing period. The methodology is optimized to retrieve not only the soil moisture content but also the albedo and the extinction coefficient of the vegetation layer. Estimated soil moisture maps produced for one year reveal high values in late spring in response to snowmelt, rainfall, and spring vegetation growth. Low values in late summer/early fall are in response to seasonal rainfall variation, increased evapotranspiration, and the end of the growing season. These results provide insights for monitoring change in complex arctic environments.