Composition alteration of stratospheric air due to sampling through a flow tube

A numerical model of a sampling tube used to conduct stratospheric air to the sampling point of a balloon-borne cryogenic whole air sampler, was developed to assess the potential effects of passage through the tube on alteration of species mixing ratios from those in the ambient. This model is based on the application of a general purpose, multireaction chemical kinetics code (CHEMSEN) to a 31 reaction (49 with heterogeneous wall loss), 23 species (41 with adsorbed or 'lost' constituents) stratospheric kinetic model, modified to take into account heterogeneous interactions with the tube wall. Effects of homogeneous gas phase chemistry and heterogeneous wall loss were estimated at three different altitudes: 15, 20, and 30 km. It was found that the gas phase chemistry was generally incapable of appreciably altering the sampled composition from that in the ambient. On the other hand, depending on the particular set of assumptions used, heterogeneous wall loss was found capable of imposing significant alterations on the sampled gas composition, particularly at altitudes above about 20 km, due to rapid radial diffusion. The expected tube wall temperature is shown to have a negligible effect on the homogeneous gas phase kinetics in the sampling tube.