This Small Business Innovation Research Phase I project concerns the development of a multi-wavelength monitor that will provide rapid, real-time measurement of the average aerosol absorption coefficient in the parcel of sample air. This monitor will employ Aerodyne's proprietary Cavity Attenuated Phase Shift spectroscopy technology in order to produce a far simpler, smaller, lower cost alternative to more traditional instruments with no loss in sensitivity or accuracy. A unique property of the proposed instrument is that it requires little or no calibration. The Phase I work plan will focus on a proof-of-principle demonstration of the proposed technique tht compares its performance with a conventional particle absorbance monitor. The Phase II project will entail constructing a field-ready prototype using the information gained in the Phase I studies and deploying the sensor on various field missions undertaken by Aerodyne's particle measurement research group. 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. The atmospheric loading of aerosols generated through human activities can exert an influence on the earth's radiation budget comparable in magnitude with greenhouse gases. The uncertainties in the current understanding of aerosol direct and indirect forcing limit the ability to quantify human influences on climate change.