Asymmetry Parameter Monitor

This proposal addresses the specific need for “new technologies or methodologies to improve the field calibration” for accurate measurements of aerosol scattering. Understanding the role that aerosols play in atmospheric radiative forcing is currently a major focus of the Department of Energy DOE) Atmospheric System Research ASR) and Atmospheric Radiation Measurement ARM) Programs. The asymmetry parameter, the ratio of the light scattered in the forward direction relative to that scattered into the backward hemisphere, is a critical optical property necessary in remote sensing, radiative transfer, and climate models. We propose to develop a commercial, state-of-the-art, portable instrument capable of measuring angular-dependent particulate scattering with high resolution; thus, providing a direct, accurate measure of the aerosol asymmetry parameter. Our proposed instrument will reduce the uncertainty in asymmetry parameter measurements and can be directly used as a field calibration of the current indirect, empirical method that DOE ARM employs as part of the Aerosol Optical Properties AOP) to derive the asymmetry parameter from filter-based absorption measurements and nephelometer backscatter measurements. Our approach is to sample particles through a circularly polarized 532 nm laser beam and collect scattered light using two position-sensitive detectors. A prototype, proof-of-concept, design has been built in Prof. Chakrabarty’s aerosol laboratory and will be the basis for the proposed instrument. The instrument will detect the scattered light from 1° to 168° simultaneously, which allows for quick and efficient procurement of data, eliminates problems regarding aerosol stability, and will provide a direct and accurate determination of the aerosol asymmetry parameter. Successfully commercialized, our instrument will provide a fundamental measure of the optical properties of ambient aerosols that will enhance the accuracy of climate change predictions and will provide a critical missing component to the DOE ARM program. Successful development and marketing of this monitor will yield a significant level of direct commercial sales from researchers in the atmospheric sciences and air quality monitoring groups. The comparatively low cost and ease of use of this sensor will allow routine measurement of the angular- dependent scattering properties of atmospheric aerosols, which is not currently available.