Collaborative Research: P2C2--Drivers for Past Variability in Tropospheric Reactive Halogens: Implications for Climate and Evaluation of Ice Core Proxies

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This project aims to examine reactive halogens and their impacts on the chemistry of the troposphere and stratosphere especially with regards to climate. Reactive halogens impact the oxidative capacity of the atmosphere thereby influencing reduced concentrations of trace gases such as methane CH4 and the abundance of short lived climate forcing agents such as ozone (O3) and aerosols in the atmosphere. Ice-core observations of the precursors and/or sinks of reactive halogens in the troposphere suggest both anthropogenic- and climate-induced changes in the abundance of reactive halogens in the troposphere. This has an, as of yet, unquantified impact on several paleoclimate proxies in ice cores.The researchers plan to investigate the sensitivity of reactive halogen abundance to anthropogenic emissions and to climate change in a global model and examine its potential feedbacks on climate. As such, the project will focus on the following two research questions: (1) What are the biggest drivers for changes in the abundance of reactive halogens over the preindustrial-industrial and glacial-interglacial timescales; and (2) What are the potential implications for the oxidizing capacity of the atmosphere and short-lived climate forcing agents CH4, tropospheric O3, and aerosols.The potential broader impacts include the potential to advance knowledge and understanding within atmospheric chemistry and climate and paleoclimatology, via potential improvement of the representation of reactive chemistry in global climate system models with interactive carbon simulation. The project supports the training graduate students in numerical modeling of atmospheric chemistry, outreach and education. It also provides for the wider community dissemination of research results of GEOS-CHEM model development through workshops and meeting sessions and public and K12 outreach and education efforts by the researchers.