ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-11723-2011 Simulated effects of changes in direct and diffuse radiation on canopy scale isoprene emissions from vegetation following volcanic eruptions Wilton D. J. 1 2 Hewitt C. N. 2 Beerling D. J. 1 Department of Animal and Plant Sciences, University of Sheffield, S10 2TN, UK Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 23 11 2011 11 22 11723 11731 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/11723/2011/acp-11-11723-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/11723/2011/acp-11-11723-2011.pdf

Volcanic eruptions can alter the quality of incoming solar irradiance reaching the Earth's surface thereby influencing the interactions between vegetation and the Earth system. Isoprene (C<sub>5</sub>H<sub>8</sub>) is a biogenic volatile organic compound emitted from leaves at a rate that is strongly dependent on the received flux of photosynthetically active radiation (PAR). We used a theoretical approach to investigate the potential for volcanic eruptions to change the isoprene flux from terrestrial forests using canopy-scale isoprene emission simulations that vary either the relative or absolute amount of diffuse (<i>I</i><sub>diff</sub>) and direct (<i>I</i><sub>dir</sub>) PAR. According to our simulations for a northern hardwood deciduous forest, if the total amount of PAR during summer remains constant while the proportion of <i>I</i><sub>diff</sub> increases, canopy-scale isoprene emissions increase. This effect increases as leaf area index (LAI) increases. Simulating a decrease in the total amount of PAR, and a corresponding increase in <i>I</i><sub>diff</sub> fraction, as measured during the 1992 Pinatubo eruption, changes daily total canopy-scale isoprene emissions from terrestrial vegetation in summertime by +2.8% and −1.4% for LAI of 6 and 2, respectively. These effects have not previously been realized or quantified. Better capturing the effects of volcanic eruptions (and other major perturbations to the atmospheric aerosol content) on isoprene emissions from the terrestrial biosphere, and hence on the chemistry of the atmosphere, therefore may require inclusion of the effects of aerosols they produce on climate and the quality of PAR.

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