Dry deposition contributes significantly to the acidification of the ecosystem. However, difficulties in measuring dry deposition of reactive gases and fine particles make routine direct monitoring impractical. An alternate approach is to use the 'concentration monitoring' method in which dry deposition is estimated from the product of measured concentration and estimated deposition velocity. To investigate sampling protocols for estimating the weekly averages of pollutant dry deposition, a sampler that performs over the period of about 0.25 to 7 days, depending on atmospheric concentrations has been developed. It consists of a Teflon cyclone to exclude particles larger than about 2 micrometers, selective solid adsorption media for reactive gases - some of which are sampled from an unstable transition flow to avoid bias from particle evaporation, and a particle filter. The sampler is the first reported application of unstable transition-flow mass transfer for the collection of trace atmospheric gases. Laboratory and limited field tests have shown that the sampler performs satisfactorily for HNO3(g) and SO2.