The first Quarterly Report is concerned with the design of an in-situ particle impactor, suitable for the trapping and classification of particles in a down flow combustor. At this early stage in the research, we are concerned with a full-scale cold flow prototype and are focusing our work on the determination of the pressure drop and the particle classification capabilities, likely to be encountered. If the pressure drop across the impactor were to be too large, the concept on an in-situ impactor would have to be discarded. The theory, rationale and final design of the cold flow impactor are described. 4 figs., 3 tabs.