Evaluation of laboratory and field performance of denuder tubes: A theoretical approach

A theoretical approach is presented for the evaluation of laboratory and field performances of denuder tubes. The Differential Technique, Asymptotic Differential Technique and Absolute Differential Technique are described as solutions to the problem of measuring a reactive species in real conditions. A method, based on the analysis of the analyte deposition pattern, is proposed for an accurate determination of the denuder loading capacity and for the formulation of sound hypothesis on the structure of the deposition function and the behaviour of the interfering species (high and low reactivity inteiferents, paniculate matter). An example of the application of this method to a field data set concerning HNO₃ collection on nylon denuders is reported. The causes of the deviation of these experimental data from the model of the Gormley and Kennedy equation are identified and discussed. The method proves to be a powerful tool for prediction of the denuder behaviour in different experimental conditions and for the interpretation of field results.