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Abstract
Abstract. A new version of the biogenic volatile organic compounds (BVOCs) emission scheme has been developed in the global vegetation model ORCHIDEE (Organizing Carbon and Hydrology in Dynamic EcosystEm), which includes an extended list of biogenic emitted compounds, updated emission factors (EFs), a dependency on light for almost all compounds and a multi-layer radiation scheme. Over the 2000–2009 period, using this model, we estimate mean global emissions of 465 Tg C yr−1 for isoprene, 107.5 Tg C yr−1 for monoterpenes, 38 Tg C yr−1 for methanol, 25 Tg C yr−1 for acetone and 24 Tg C yr−1 for sesquiterpenes. The model results are compared to state-of-the-art emission budgets, showing that the ORCHIDEE emissions are within the range of published estimates. ORCHIDEE BVOC emissions are compared to the estimates of the Model of Emissions of Gases and Aerosols from Nature (MEGAN), which is largely used throughout the biogenic emissions and atmospheric chemistry community. Our results show that global emission budgets of the two models are, in general, in good agreement. ORCHIDEE emissions are 8 % higher for isoprene, 8 % lower for methanol, 17 % higher for acetone, 18 % higher for monoterpenes and 39 % higher for sesquiterpenes, compared to the MEGAN estimates. At the regional scale, the largest differences between ORCHIDEE and MEGAN are highlighted for isoprene in northern temperate regions, where ORCHIDEE emissions are higher by 21 Tg C yr−1, and for monoterpenes, where they are higher by 4.4 and 10.2 Tg C yr−1 in northern and southern tropical regions compared to MEGAN. The geographical differences between the two models are mainly associated with different EF and plant functional type (PFT) distributions, while differences in the seasonal cycle are mostly driven by differences in the leaf area index (LAI). Sensitivity tests are carried out for both models to explore the response to key variables or parameters such as LAI and light-dependent fraction (LDF). The ORCHIDEE and MEGAN emissions are differently affected by LAI changes, with a response highly depending on the compound considered. Scaling the LAI by a factor of 0.5 and 1.5 changes the isoprene global emission by −21 and +8 % for ORCHIDEE and −15 and +7 % for MEGAN, and affects the global emissions of monoterpenes by −43 and +40 % for ORCHIDEE and −11 and +3 % for MEGAN. Performing a further sensitivity test, forcing ORCHIDEE with the MODIS LAI, confirms the high sensitivity of the ORCHIDEE emission module to LAI variation. We find that MEGAN is more sensitive to variation in the LDF parameter than ORCHIDEE. Our results highlight the importance and the need to further explore the BVOC emission estimate variability and the potential for using models to investigate the estimated uncertainties.
Highlights
The terrestrial biosphere emits large amounts of volatile organic compounds (VOCs) in particular terpenoids, such as isoprene, monoterpenes and sesquiterpenes, and oxygenated hydrocarbons such as methanol, acetone, formaldehyde, acetaldehyde, acetic acid or formic acid (Laothawornkitkul et al, 2009; Guenther et al, 2012a; Penuelas and Staudt, 2010)
Using reanalysis provided by Qian et al (2006) as climate forcings for the year 2000, Guenther et al (2012a) report Biogenic volatile organic compounds (BVOCs) emissions of 472 Tg C yr−1 for isoprene, 124 Tg C yr−1 for monoterpenes and 11.5 Tg C yr−1 for acetaldehyde
To isolate the signal related to the light-dependent fraction (LDF), we investigate the hourly variation of two “test compounds”, the first defined as light-independent (LDF = 0) and the second defined as totally light-dependent (LDF = 1)
Summary
The terrestrial biosphere emits large amounts of volatile organic compounds (VOCs) in particular terpenoids, such as isoprene, monoterpenes and sesquiterpenes, and oxygenated hydrocarbons such as methanol, acetone, formaldehyde, acetaldehyde, acetic acid or formic acid (Laothawornkitkul et al, 2009; Guenther et al, 2012a; Penuelas and Staudt, 2010). Biogenic volatile organic compounds (BVOCs) play a central role in atmospheric chemistry, influencing the oxidative capacity of the atmosphere (Arneth et al, 2011; Taraborrelli et al, 2012), leading to the production of tropospheric ozone in the presence of nitrogen oxides (Von Kuhlmann et al, 2003; Mao et al, 2013), and influencing the tropospheric carbon monoxide budget (Pfister et al, 2008). Despite numerous measurements and the progressive understanding of the processes underlying their production, BVOC emission estimates are still highly uncertain, and vary significantly (Steiner and Goldstein, 2007; Arneth et al, 2008; Simpson et al, 2012; Sindelarova et al, 2014)
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