An acidic pollutant sampler for dry deposition monitoring has been designed and evaluated in laboratory and field studies. The system, which is modular and simple to operate, samples gaseous HNO3, NH3, SO2 and NO2 and particulate SO4(-2), NO3(1-) and NH4(1+) and is made of Teflon to minimize trace reactive gas sorption. Particles greater than about 2 micrometers are removed with a cyclone. A transition-flow reactor (TFR) Teflon tube contains a Nylon liner for collection of a constant fraction of gaseous HNO3 and a Nafion liner for collection of a constant fraction of NH3. Excellent results were obtained in week-long runs with parallel sampling. In the first seven of these week-long runs the average difference between samples for gaseous HNO3 was 4.6% with a standard deviation of only 3.7. In the same sampling runs, the average difference for particulate sulfate was 3.0% with a standard deviation of only 1.4.