The design and construction of eight 1-m3 fumigation chambers for exposing plants to reactive air pollutants at low concentrations are reported. Teflon surfaces are used where possible to minimize the adsorption, absorption, desorption and chemical reaction of the pollutants. A purified ambient air supply, to which metered quantities of gaseous pollutants are added, is used to give two air changes per minute at constant, low, pollutant concentrations. Comparative analysis of the chambers indicates that conditions may be maintained with a significant degree of precision, i.e. temperature ±0.3°C, RH ±6%, light intensity ±5 μmol m−2 s−1. Boundary layer analysis from models of cherry tree (Prunus avium) leaves indicate that the minimum conductance value within these chambers is 2 cm s−1.