This Quarterly Report is concerned with the design and operation of the hot flow impactor, suitable for insertion in the downflow combustor. An in-situ impactor was necessary for two reasons. First, it allows prior removal of large particles, which are likely to clog the high velocity sampling probe, especially under fuel rich gasification conditions. Second, it provides a method for sampling, in an in-situ manner, large particles for further analysis. 8 figs.