Chlorinated Very Short-Lived Substances:Modelling their global emissions and impact on stratospheric ozone
Year: 2021
Type: dissertation
Abstract: Since the discovery of the damaging effects of chlorofluorocarbons, stratospheric ozone has been studied extensively in the last 50 years. While the Montreal Protocol and amendments have largely nullified the threat from long-lived ozone-depleting gases, emerging evidence suggests uncontrolled chlorinated compounds, Very Short-Lived Substances (Cl-VSLS), present a barrier to timely ozone recovery. This thesis extends scientific understanding of Cl-VSLS emissions and impacts, combining observations, inversion methods and a 3-D chemistry transport model. This work calculates policy-relevant ozone depletion potentials (ODPs) of four Cl-VSLS (CH2Cl2, CHCl3, C2Cl4, C2H4Cl2) using a troposphere-stratosphere modelling system. The influence of emission location and season on the ODPs is investigated. Whilst little seasonal variability exists, the location of emissions exerts a strong influence, with the largest ODPs due to Tropical Asian emissions. Chloroform (CHCl3) and dichloromethane (CH2Cl2) have the largest ODPs (up to ~0.02-0.03), comparable to some long-lived halocarbons restricted by the Montreal Protocol. A synthesis inversion is used to calculate regional Cl-VSLS fluxes based on minimising differences between modelled and observed abundances with prior constraints. Over 2007-2017, global CH2Cl2 emissions increase significantly due to increasing Asian emissions, while C2Cl4 emissions decrease, from diminishing uses in Europe and North America. The emissions are evaluated and provide a good match to assimilated observations and those independent to the inversion. Stratospheric impacts of Cl-VSLS are investigated using time-varying emissions. The stratospheric input of chlorine from Cl-VSLS and products increased by 43% between 2007 and 2017, from 92.3 ± 5.0 ppt Cl to 132.1 ± 8.9 ppt Cl. Stratospheric model simulations show marked decrease in lower stratospheric ozone due to Cl-VSLS. In 2017, over Antarctica, Cl-VSLS reduced lower stratospheric ozone by 1.2% and the global mean column reduction was 0.4% (-1.2 DU). Increasing Asian emissions indicate potential for greater future impacts. Hence, Cl-VSLS should continue to be monitored.
Author: Tom Claxton
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
Awards: Oceanic Reactive Carbon: Chemistry-Climate impacts (ORC3), Co-ordinated Airborne Studies in the Tropics (CAST), THIS PROPOSAL SEEKS FIVE YEARS OF CONTINUING FUNDING FOR THE MULTINATIONAL, GLOBAL ATMOSPHERIC MEASUREMENT PROGRAM ENTITLED ADVANCED GLOBAL ATMOSPHER, Sources and Impacts of Short-Lived Anthropogenic Chlorine, G4503768103, Project Science Activities and Trace Gas Investigations from Whole Air Sampling on the NCAR GV Aircraft During the Convective Transport of Active Species in the Tropics Experiment, The Impact of Short-Lived Halocarbons on Ozone and Climate (ISHOC): An International Multi-Model Intercomparison, THIS PROPOSAL SEEKS FIVE YEARS OF CONTINUING FUNDING FOR THE MULTINATIONAL GLOBAL ATMOSPHERIC MEASUREMENT PROGRAM ENTITLED ADVANCED GLOBAL ATMOSPHERIC GASES EXPERIMENT (AGAGE). THE CASE FOR REAL-TIME HIGH-FREQUENCY MEASUREMENT NETWORKS IS VERY STRONG AND THE OBSERVATIONS AND THEIR INTERPRETATION ARE RECOGNIZED WIDELY FOR THEIR IMPORTANCE TO OZONE DEPLETION AND CLIMATE CHANGE STUDIES AND TO VERIFICATION ISSUES ARISING FROM THE MONTREAL (OZONE) AND KYOTO AND SUCCESSOR (CLIMATE) PROTOCOLS.AGAGE IS DISTINGUISHED BY ITS CAPABILITY TO MEASURE GLOBALLY AT HIGH FREQUENCY ALL THE IMPORTANT SPECIES IN THE MONTREAL PROTOCOL AND ALL THE IMPORTANT NON-CO2 GASES IN THE KYOTO PROTOCOL. THE SCIENTIFIC OBJECTIVES OF AGAGE ARE IMPORTANT IN FURTHERING UNDERSTANDING OF GLOBAL CHEMICAL AND CLIMATIC PHENOMENA. THEY ARE:1) DETERMINE OPTIMALLY FROM OBSERVATIONS THE GLOBAL RATES OF EMISSION AND/OR DESTRUCTION (I.E. LIFETIME) OF ANTHROPOGENIC CHLOROCARBONS CHLOROFLUOROCARBONS (CFCS) BROMOCARBONS HYDROCHLOROFLUOROCARBONS (HCFCS) HYDROFLUOROCARBONS (HFCS) AND PERFLUORINATED COMPOUNDS (PFCS NF3 AND SF6) THAT CONTRIBUTE MOST OF THE REACTIVE HALOGEN TO THE STRATOSPHERE AND/OR ARE STRONG INFRARED ABSORBERS.(2) DOCUMENT ACCURATELY THE GLOBAL DISTRIBUTIONS AND TEMPORAL BEHAVIORS OF BIOGENIC/ANTHROPOGENIC GASES IMPORTANT IN CLIMATE CHANGE AND/OR OZONE DEPLETION: METHANE NITROUS OXIDE CARBON MONOXIDE HYDROGEN METHYL CHLORIDE AND METHYL BROMIDE.(3) IDENTIFY GREENHOUSE AND OZONE-DEPLETING GASES (E.G. SO2F2 NF3 C4F10 C5F12 C6F14 C7F16 AND C8F18 HAVE BEEN IDENTIFIED) INITIATE REAL-TIME MONITORING OF THESE GASES AND RECONSTRUCT THEIR PAST HISTORIES FROM AGAGE AND AIR-ARCHIVE MEASUREMENTS.(4) DETERMINE OPTIMALLY THE AVERAGE CONCENTRATIONS AND TRENDS OF TROPOSPHERIC HYDROXYL RADICALS FROM THE RATES OF DESTRUCTION OF ATMOSPHERIC METHYL CHLOROFORM HFCS AND HCFCS AND ESTIMATES OF THEIR EMISSIONS.(5) DETERMINE OPTIMALLY FROM ATMOSPHERIC OBSERVATIONS AND ESTIMATES OF THEIR DESTRUCTION RATES THE MAGNITUDES AND DISTRIBUTIONS BY REGION OF SURFACE SOURCES/SINKS OF THESE GASES.(6) PROVIDE ACCURATE DATA ON THE GLOBAL ACCUMULATION OF THESE TRACE GASES WHICH ARE USED TO TEST THE SYNOPTIC/REGIONAL/GLOBAL-SCALE CIRCULATIONS PREDICTED BY THREE-DIMENSIONAL MODELS.(7) PROVIDE GLOBAL AND REGIONAL MEASUREMENTS OF METHANE CARBON MONOXIDE AND HYDROGEN AND ESTIMATES OF HYDROXYL LEVELS TO TEST PRIMARY ATMOSPHERIC OXIDATION PATHWAYS AT MID-LATITUDES AND THE TROPICS., Aerosol-Cloud Coupling And Climate Interactions in the Arctic, Climate and Air Quality Impact of Airborne Halogens, WE PROPOSE TO STUDY THE ORGANIC TRACE GAS COMPOSITION FROM A VARIETY OF SAMPLING PLATFORMS TO ADDRESS SCIENTIFIC QUESTIONS RELATED TO UNDERSTANDING A
OpenAlex ID: W3157960084