Simulated effects of changes in direct and diffuse radiation on canopy scale isoprene emissions from vegetation following volcanic eruptions D. J. Wilton1,2, C. N. Hewitt2, and D. J. Beerling1 1Department of Animal and Plant Sciences, University of Sheffield, S10 2TN, UK 2Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
Abstract. 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 (C5H8) 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 (Idiff) and direct (Idir) 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
Idiff 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 Idiff 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.
Citation: Wilton, D. J., Hewitt, C. N., and Beerling, D. J.: Simulated effects of changes in direct and diffuse radiation on canopy scale isoprene emissions from vegetation following volcanic eruptions, Atmos. Chem. Phys., 11, 11723-11731, doi:10.5194/acp-11-11723-2011, 2011.