Abstract
Abstract. A biogenic emission scheme based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.1 (Guenther et al., 2012) has been integrated into the ECHAM6-HAMMOZ chemistry climate model in order to calculate the emissions from terrestrial vegetation of 32 compounds. The estimated annual global total for the reference simulation is 634 Tg C yr−1 (simulation period 2000–2012). Isoprene is the main contributor to the average emission total, accounting for 66 % (417 Tg C yr−1), followed by several monoterpenes (12 %), methanol (7 %), acetone (3.6 %), and ethene (3.6 %). Regionally, most of the high annual emissions are found to be associated with tropical regions and tropical vegetation types. In order to evaluate the implementation of the biogenic model in ECHAM-HAMMOZ, global and regional biogenic volatile organic compound (BVOC) emissions of the reference simulation were compared to previous published experiment results with MEGAN. Several sensitivity simulations were performed to study the impact of different model input and parameters related to the vegetation cover and the ECHAM6 climate. BVOC emissions obtained here are within the range of previous published estimates. The large range of emission estimates can be attributed to the use of different input data and empirical coefficients within different setups of MEGAN. The biogenic model shows a high sensitivity to the changes in plant functional type (PFT) distributions and associated emission factors for most of the compounds. The global emission impact for isoprene is about −9 %, but reaches +75 % for α-pinene when switching from global emission factor maps to PFT-specific emission factor distributions. The highest sensitivity of isoprene emissions is calculated when considering soil moisture impact, with a global decrease of 12.5 % when the soil moisture activity factor is included in the model parameterization. Nudging ECHAM6 climate towards ERA-Interim reanalysis has an impact on the biogenic emissions, slightly lowering the global total emissions and their interannual variability.
Highlights
The majority of volatile organic compounds emitted from the terrestrial biosphere (BVOCs), including hydrocarbons as well as oxygenated organic compounds, are highly reactive and have been shown to affect both gas-phase and heterogeneous atmospheric chemistry at local and global scales (Ashworth et al, 2013)
A biogenic emission scheme based on MEGANv2.1 (Guenther et al, 2012) has been integrated into the ECHAM6HAMMOZ chemistry climate model and linked to parameters of the JSBACH vegetation model, in order to calculate the biogenic emissions of 32 compounds
Model estimates of biogenic volatile organic compound (BVOC) emissions show a large variation, global isoprene emissions varying within a factor of 1.6, when global monoterpene and methanol emissions vary within a factor of about 3.5
Summary
The majority of volatile organic compounds emitted from the terrestrial biosphere (BVOCs), including hydrocarbons (isoprene, monoterpenes, and sesquiterpenes) as well as oxygenated organic compounds, are highly reactive and have been shown to affect both gas-phase and heterogeneous atmospheric chemistry at local and global scales (Ashworth et al, 2013). BVOCs are a crucial component of the Earth system that has to be considered in global and regional chemical transport models Quantitative estimates of their emissions into the atmosphere are needed for numerical assessments of their impacts on past, present, and future air quality and climate (Sindelarova et al, 2014). The aim of the present study is (i) to present the updated version of the biogenic emission module implemented in ECHAM6HAMMOZ, (ii) to evaluate present-day global- and regionalscale emissions for a series of 32 compounds, (iii) to compare MEGAN–ECHAM-HAMMOZ basic results to previous offline and online experiment results with MEGAN, and (iv) to test the sensitivity of BVOC emissions to climate- and vegetation-dependent model parameters
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