Evaluation of 14CO as a Tracer of OH in a Global Model

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• Liam Blyth – Imperial College London
• Tuesday 21 November 2023, 11:30-12:30
• Chemistry Dept, Unilever Lecture Theatre and Zoom.

If you have a question about this talk, please contact Vichawan (Print) Sakulsupich.

Last talk of term

The Hydroxyl Radical (OH) is one of the most important species in atmospheric chemistry due to its role in controlling the lifetime of CH4 and several atmospheric pollutants. Due to its high reactivity, OH has a lifetime of ~1 second, making it challenging to measure. As a result, a proxy species is needed to estimate OH’s temporal and spatial variability. Historically this was done using Methyl Chloroform (MCF), however, a recent decline in the atmospheric mixing ratio of MCF motivates us to seek an alternative proxy. Here we present the results of global 14CO simulations and investigate its ability to determine the spatial and temporal trends in OH. Simulated 14CO agrees within a few molecules cm-3 with measurements at various locations, and shows the clear trends seen in measured data. Simulations show local 14CO concentrations have a reliance on hemispheric, rather than local OH trends, particularly in the higher latitudes, implying it has the ability to capture trends on this scale. Our results also show that a large-scale measurement campaign at an individual site at mid-latitude (Mace Head) could have detected the 10% increase in OH burden in the NH simulated over the last 35 years in the model. To investigate this, a new approach is developed to remove the effect of the solar cycle on 14CO concentrations, allowing long-term trends to be better analysed. Our simulations, in conjunction with global measurements, have the potential to solve the recent disparity between OH trends seen in atmospheric models and measurement data.

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Topic: CAS seminar: Liam Blyth Time: Nov 21, 2023 11:30 AM London

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