Impacts of HOx regeneration and recycling in the oxidation of isoprene: Consequences for the composition of past, present and future atmospheres
A global chemistry-climate model is used to assess the impact on atmospheric composition of the regeneration and recycling of HOx in the photo-oxidation of isoprene. The impact is explored subject to present-day, pre-industrial and future climate/emission scenarios. Our calculations show that, in all cases, the inclusion of uni-molecular isomerisations of the isoprene hydroxy-peroxy radicals leads to enhanced production of HOx radicals and ozone. The global burden of ozone increases by 25–36 Tg (8–18%), depending on the climate/emissions scenario, whilst the changes in OH lead to decreases in the methane lifetime of between 11% in the future and 35% in the pre-industrial. Critically the size of the change in methane lifetime depends on the VOC/NOx emission ratio. The results of the present-day calculations suggest a certain amount of parameter refinement is still needed to reconcile the updated chemistry with field observations (particularly for HO2+RO2). However, the updated chemistry could have far-reaching implications for: future-climate predictions; projections of future oxidising capacity; and our understanding of past changes in oxidising capacity.
Authors: Archibald, A.T., Levine, James G., Abraham, N.L., Cooke, M.C., Edwards, P.M., Heard, D.E., Jenkin, M.E., Karunaharan, A., Pike, R.C., Monks, P.S., Shallcross, D.E., Telford, P.J., Whalley, L.K., Pyle, J.A.