Preliminary assessment of chlorine reactivity with environmental materials accounting for boundary layer and maximum deposition effects. (1st July 2021)

• Record Type: Journal Article
• Authors: Spicer, Thomas O.; Fox, Shannon B.; Hicks, Bruce B.
• Is Part Of: Atmospheric environment. Volume 256(2021)
• Publication Date: 2021-07-01
• Subjects: Dry deposition -- Boundary layer resistance -- Chlorine -- Maximum deposition; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2021.118274
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Many toxic industrial chemicals (TICs) such as chlorine and ammonia are very reactive with commonly encountered materials in the environment. The amount of TIC material reacted in the environment is an important factor in determining the impact of a release. Typically characterized with a dry deposition rate in atmospheric dispersion models, the reaction rate has predominately been studied in field scale experiments at concentration levels typical for air pollution (ppm levels). When considering the removal of chlorine by (dry) deposition in an episodic release, gas phase concentrations will be much higher than those associated with air pollution, and near-field reaction of chlorine with local vegetation will be strongly influenced by the response of leaves and other elements of the surface "canopy" to those high concentrations. In this work, standard engineering methods characterizing the rate of mass transfer from a fluid to a surface in conjunction with reaction at that surface are applied. Previous experimental programs that studied the removal of chlorine under conditions relevant to this study show that deposition of chlorine to plant material can reach a limiting maximum so that the plant material can no longer react with gaseous chlorine despite continued exposure. In the analysis presented here, it is shown that the effect of the maximum deposition can be treated using the same approach as has been used to model catalyst poisoning. This study developed a model to account for boundary layer resistance and the impact of maximum deposition in a framework that could be incorporated in atmospheric dispersion models. To test the efficacy of this model, the Controlled Environment Reactivity Test (CERT) apparatus was designed to expose selected environmental materials (substrates including soil, rye grass, white clover, maple leaves, and spruce branches) to chlorine with initial concentration of (nominally) 1000 ppm where the gas phase chlorine concentration can be measured as a function of time to determine relevant modeling parameters. The apparatus was built to control the flow velocity of the chlorine/air mixture over the experimental substrates with turbulence levels that are comparable to the atmosphere. Model parameters were found for the environmental materials tested. Highlights: Chlorine dry deposition is limited by a maximum and depends on the material. Model developed for chlorine dry deposition with surface kinetics and deposition. Experimental results for sample surfaces presented.