Volcanic research is a significant part of the "Earth Surface & Interior" focus area of the NASA Earth Science program. After a volcanic eruption, the smallest ash particles can remain in the atmosphere for days to months affecting public health in the surrounding regions and the radiation balance on Earth. Airborne volcanic ash particulate matter (PM) also poses a major threat to aviation and would therefore be essential to distinguish and identify by remote sensing and in situ techniques. Vista Photonics in collaboration with New Jersey Institute of Technology proposes to develop an innovative technology for in situ characterization of PM in volcanic plumes, including measurement of PM size distribution function and concentration. The Phase I study will demonstrate the feasibility of the proposed technology and outline the design of the Phase II prototype instrument. The successful completion of this program will lead to development of a very inexpensive compact PM measurement instrument suitable for use on a variety of ground based and airborne platforms including remotely operated aircraft and surface craft, and even disposable devices, such as dropsondes.