Inexpensive, reliable, accurate means are needed to monitor SO2 and NO2 in the atmosphere. Sulfation and nitration plates have been used with varying degrees of acceptance for two decades. These devices are exposed for a period of time where the pollutant in the surrounding ambient air reacts with the reactive surface of the monitor. The monitor is then returned to the laboratory where a chemical determination of the reaction product is made. By considering the duration of exposure and the reactive surface area, a product flux is determined. The product flux is used along with a calibration factor (CF) to estimate the gas-phase concentration of the pollutant. Historically the calibration factor, which relates ambient air pollutant concentration to product flux, has been assumed to be constant. The objectives of the study are to evaluate the performance of commercial sulfation and nitration plates. The study is designed to determine the sensitivity of plate calibration factors to pollutant concentration, simulated wind speed, humidity, and temperature.