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Modelling of atmospheric chlorine and its effect on volatile organic compounds

Ivatt, Peter (2017) Modelling of atmospheric chlorine and its effect on volatile organic compounds. MSc by research thesis, University of York.

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Abstract

This study uses a recently developed halogen scheme (Sherwen et al., 2016) for the GEOSChem chemical transport model to perform and in-depth investigation into tropospheric atomic chlorine. In the study we find a global atomic Cl average concentration of 495 cm-3 with the highest concentrations of 1 – 5.5 x 104 cm-3 being located in the tropical marine boundary layer in tropical regions with a preference towards the north hemisphere. Globally the reaction between HOBr and HCl on sulfate aerosol dominates the production of Cl (77 %) precursors through its production of BrCl but in the boundary layer sea-salt sources through reaction with N2O5 or iodine species can dominate, particularly in polluted coastal regions. HCl is globally the dominant Cly species (80.9 %) but in the boundary layer other compounds (notably ClNO2) can play a significant role. The rate of heterogeneous processing determines the ratio of HCl to more active Cly components. The model agrees with previous studies that Cl is a small sink compared to the OH sink (0.9 %). However, the Cl sink relative to the OH sink for ethane and propane is a more significant 15% and 6.5% respectively. There is a high degree of regional variability in the Cl removal of ethane, with the removal rising over the northern hemisphere oceans to ~50 % of OH removal at sea level and ~30 % averaged over whole column. Between 1998 and 2008 Cl concentrations increase globally due to developing regions experiencing increased Cl production due to increased concentration of pollutants NOx and SO42- and developed regions experiencing reduced loss due to decreases in NMVOC emissions. With the exception being Africa which as seen an increase in loss with minimal increase in production.

Item Type: Thesis (MSc by research)
Academic Units: The University of York > Chemistry (York)
Depositing User: Mr Peter Ivatt
Date Deposited: 07 Sep 2017 09:03
Last Modified: 07 Sep 2017 09:03
URI: http://etheses.whiterose.ac.uk/id/eprint/17851

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