Experimental Techniques for Studying Surface Chemistry in Smog Chambers

Chemical reactions occurring on the walls of environmental chambers provide a large fraction of the radical species which initiate gas phase smog chemistry, but the nature and magnitude of these processes have not received focused attention. For example, the empirical models used in conjunction with the UNC and Riverside smog chambers contain different reaction schemes and product distributions for the adsorption and reaction of NO2 on surfaces. In addition, several parameters are often adjusted empirically when environmental chamber data is analyzed. The current understanding of wall chemistry and its parameterization in models are briefly reviewed here. Determination of the fundamental processes involved in wall reactions is needed for prediction of heterogeneous radical generation in different chambers under a variety of conditions. Techniques available for quantitative study of these heterogeneous processes include Knudsen cell, flow tube, and aerosol methods. The use of these methods in our laboratory is demonstrated, and their applicability to the study of environmental chamber wall processes is discussed.