CAPS-Based Particle Single Scattering Albedo Monitor

Aerosol particles affect the radiative balance of the earth directly, by scattering and absorbing solar and terrestrial radiation, and indirectly, by acting as cloud condensation nuclei. It is now recognized that atmospheric loading of aerosols, generated through human activities, can exert an influence on the earth¿s radiation budget comparable in magnitude with greenhouse gases. However, uncertainties in the understanding of both direct and indirect aerosol forcing limit the ability to quantify human influences on climate change. This project will develop a particle single scattering albedo monitor that combines extinction and scattering measurements in one instrument, with rapid time-response, active temperature/relative humidity control, and high sensitivity. This monitor will provide a simpler, smaller, lower cost alternative to cavity ring downbased systems and more traditional instruments with no loss in sensitivity or accuracy. In Phase I, a laboratory prototype was constructed and calibrated. Both particle extinction and absorption coefficients were measured simultaneously using monodisperse polystyrene latex particles ranging in size from 0.1 to 8.0 microns in diameter. A baseline precision for the extinction measurement was ~0.3 Mm-1 in 60 seconds integration time. The monitor¿s response to scattering was flat for particles from 0.1 to 2 microns, but fell to 75% of full response at 8 microns. Modeling indicated that the falloff was caused by use of a highly non-ideal integrating volume. Phase II will develop a robust and improved prototype instrument, which will be compared to a number of commercially available instruments. Once its performance capabilities have been established, the prototype will be used in the field to measure aircraft exhaust and urban air pollution.Commercial Applications and Other Benefits as described by the awardee: The comparatively low cost and ease of use of this sensor should allow almost routine measurement of the scattering properties of atmospheric aerosols, something precluded by the cost and complexity of current instrumentation. Commercial sales should be expected from the atmospheric sciences and environmental pollution research and development communities.