Effect of dry deposition of NOx and SO2 gaseous pollutants on the degradation of calcareous building stones |
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| Institution: | 1. Electrical and Computer Engineering Department, Northeastern University, Boston, MA, USA;2. Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA;1. Department of Electrical Engineering, Biomedical Signal and Image Processing Laboratory (BiSIPL), Sharif University of Technology, Tehran, Iran;2. Control and Intelligent Processing Center of Excellence (CIPCE), School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran;3. School of Cognitive Sciences, Institute for Research in Fundamental Sciences (IPM), Tehran, Iran;4. Image Analysis Laboratory, Departments of Radiology and Research Administration, Henry Ford Health System, Detroit, Michigan, USA;1. Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, Québec, H3A 0B9 Canada;2. Department of Mathematics and Statistics, McGill University, Montréal, Québec, H3A 0B9 Canada;1. Department of Applied Mathematics, Northwestern Polytechnical University, Xi’an 710072, PR China;2. NPU-UoG International Cooperative Lab for Computation & Application in Cardiology, Northwestern Polytechnical University, Xi’an 710072, PR China;3. Department of Mechanics, Beijing Institute of Technology, Beijing 100081, PR China;1. Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Veterinary Public Health, Division of Pharmacology and Toxicology, Box 7028, SE-750 07 Uppsala, Sweden;2. DMPK Modeling & Simulation, Oncology IMED, AstraZeneca, Waltham, MA 02151, USA;3. Mathematical Institute, Leiden University, PB 9512, 2300 RA Leiden, The Netherlands |
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| Abstract: | A laboratory-based atmospheric flow chamber, using realistic presentation rates of SO2, NO and NO2 pollutants directed to various dry and wetted surfaces, has been employed to quantify the effects of the individual pollutants and the role of ozone as an oxidant. For the individual pollutant gases reacting with stone surfaces coming to equilibrium with 84% relative humidity (r.h.), chemical reaction in the presence of a moisture film proceeds and the extent of this reaction is related to pollutant gas solubility in the moisture film, i.e. SO2 > NO2 > NO. After dissolution in the moisture film, the pollutant gases are oxidized in the presence of catalysts associated with the stones. The additional presence of ozone promotes oxidation of the pollutant gases and thus their reaction with the stones. For SO2 pollutant, oxidation in the gas phase is not significant compared with that in the moisture film, with enhanced oxidation in the presence of catalysts. Ozone increases oxidation of NO and NO2 pollutant gases in the gas phase and moisture film; however, the oxidation of SO2 in the moisture film is more significant than that of NO or NO2. Wetting of the stone surfaces, in the absence of ozone, reveals the consistently greatest chemical reaction with SO2 compared with NO and NO2, which is related to SO2 solubility, oxidation in the presence of catalysts and production of sulphuric acid. Generally similar behaviour is evident of NO and NO2, but NO shows a reduced extent of chemical reaction, implying that its oxidation in surface water, in the presence of catalytic species, is slow and hence the reactants are lost in the form of run-off. In the additional presence of ozone, the SO2 pollutant gas gives rise to enhanced chemical reaction, whereas both NO and NO2 show lower extents of chemical reaction than for the dry stones. This arises from the relatively slow conversion of N2O5 in the liquid phase to nitric acid, allowing loss of reactants in run-off. |
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