Interpretation of uptake coefficient data obtained with flow tubes.

The uptake of trace gases such as OH and HO2 radicals, NH3, ClONO2, N2O5, ozone, and many other gases by water, aqueous solutions of acids, and salts has been reported by numerous investigators using a variety of techniques. Reported uptake coefficients vary greatly, ranging from 10(-8) to 1. This paper describes a new analysis of uptake data obtained in flow tubes that consolidates data obtained for various flow rates and trace gas concentrations. Previous analyses, which have been often used, are shown to be limiting cases or special cases of the analysis outlined here. Of particular emphasis are results for wetted-wall columns and trace gas uptake by aerosol entrained in flow tubes. In the absence of aerosol, the analysis is shown to predict the decrease in trace gas concentration due to bulk chemical reaction and/or reaction at the tube wall or gas-liquid interface. Uptake coefficients for OH and HO2 radicals on water in wetted-wall tubes are shown to range from 0.01 to 1, and on sulfuric acid, they vary from 0.008 to 0.03. For O3 on a water film doped with a scavenger, the uptake coefficient is found to be 0.0008. Uptake coefficients determined by different techniques are compared.