12 Dec 2022
12 Dec 2022
Status: this preprint is open for discussion.

Updated Isoprene and Terpene Emission Factors for the Interactive BVOC Emission Scheme (iBVOC) in the United Kingdom Earth System Model (UKESM1.0)

James Weber1, James A. King1, Katerina Sindelarova2, and Maria Val Martin1,3 James Weber et al.
  • 1School of Biosciences, University of Sheffield, Sheffield, S10 2TN, UK
  • 2Department of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
  • 3Leverhulme Centre for Climate Change Mitigation, School of Biosciences, University of Sheffield, S10 2TN, Sheffield, UK

Abstract. Emissions of biogenic volatile organic compounds (BVOCs) influence atmospheric composition and climate and will be influenced by future changes in land use and land cover (LULC) and change. Climate and Earth System Models typically calculate emissions using parameterisations involving surface temperature, photosynthetic activity, CO2 and the type of vegetation present. The influence of vegetation is described by assigning emission factors (EF) to different types of vegetation simulated in the model. We detail calculations of new EF for the Interactive BVOC Emission Scheme (iBVOC) used in the United Kingdom Earth System Model (UKESM). These EFs are based on those used by the Model of Emissions of Gases and Aerosols from Nature (MEGAN) v2.1 scheme.

We present these EFs as alternatives to the current EFs used in iBVOC which are derived from older versions of MEGAN and the Organizing Carbon and Hydrology in Dynamic Ecosystem (ORCHIDEE) emission scheme. The EFs currently used by iBVOC include an oversimplification which incorporates the EF of shrubs (high isoprene emitters) into the EFs for C3 and C4 grasses (low isoprene emitters) despite UKESM1 treating grasses and shrubs separately. Thus, the current approach significantly overestimates the isoprene emissions from grasses, particularly C4 grass which is responsible for 40 % of total simulated isoprene emissions in the present day, much higher than other estimates of ~0.3–10 %.

The new isoprene EF calculated in this work substantially reduce the amount of isoprene emitted by C4 grassland, in line with observational studies and other modelling approaches, while also increasing the emissions from known sources such as tropical broadleaf trees. Similar results are found from the change to terpene EF.

The total global isoprene and terpene emissions with the new EF are in the range suggested by literature. The existing model biases in isoprene column are slightly exacerbated with the new EFs although other drivers of this bias are also noted. The disaggregation of shrub and grass EFs should lead to a more faithful description of the contribution to BVOC emissions from different vegetation types, critical for understanding BVOC emissions in the pre-industrial and under different future LULC scenarios such as those including wide scale reforestation or deforestation.

James Weber et al.

Status: open (until 22 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-748', Anonymous Referee #1, 11 Jan 2023 reply

James Weber et al.


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Latest update: 03 Feb 2023
Short summary
The emissions of volatile organic compounds from vegetation (BVOCs) influence atmospheric composition and the contribute to certain gases and aerosols (tiny airborne particles) which play a role in climate change. BVOC emissions are likely to change in the future due to changes in climate and land use. Therefore, accurate simulation of BVOC emission is important and this study describes an update to the simulation of BVOC emissions in the United Kingdom Earth System Model (UKESM).