Abstract
Abstract. The Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1) together with the Modern-Era Retrospective Analysis for Research and Applications (MERRA) meteorological fields were used to create a global emission data set of biogenic volatile organic compounds (BVOC) available on a monthly basis for the time period of 1980–2010. This data set, developed under the Monitoring Atmospheric Composition and Climate project (MACC), is called MEGAN–MACC. The model estimated mean annual total BVOC emission of 760 Tg (C) yr−1 consisting of isoprene (70%), monoterpenes (11%), methanol (6%), acetone (3%), sesquiterpenes (2.5%) and other BVOC species each contributing less than 2%. Several sensitivity model runs were performed to study the impact of different model input and model settings on isoprene estimates and resulted in differences of up to ±17% of the reference isoprene total. A greater impact was observed for a sensitivity run applying parameterization of soil moisture deficit that led to a 50% reduction of isoprene emissions on a global scale, most significantly in specific regions of Africa, South America and Australia. MEGAN–MACC estimates are comparable to results of previous studies. More detailed comparison with other isoprene inventories indicated significant spatial and temporal differences between the data sets especially for Australia, Southeast Asia and South America. MEGAN–MACC estimates of isoprene, α-pinene and group of monoterpenes showed a reasonable agreement with surface flux measurements at sites located in tropical forests in the Amazon and Malaysia. The model was able to capture the seasonal variation of isoprene emissions in the Amazon forest.
Highlights
Non-methane volatile organic compounds (VOCs) are released into the atmosphere as a result of anthropogenic activity as well as biochemical processes in soils, oceans and vegetation
Comparison of the three methods to derive photosynthetically active radiation (PAR) is shown in Fig. 7: the annual mean PAR from the ModernEra Retrospective Analysis for Research and Applications (MERRA) data set is compared with PAR provided by University of Maryland and with PAR calculated as half of incoming shortwave radiation
The sensitivity simulations led to total annual isoprene emissions within ±17 % of the reference simulation, except for the S4 simulation introducing the soil moisture effect, which led to a 50 % decrease in the isoprene emission
Summary
Non-methane volatile organic compounds (VOCs) are released into the atmosphere as a result of anthropogenic activity as well as biochemical processes in soils, oceans and vegetation. The first model version (Guenther et al, 1995) considered the effect of both light and temperature on isoprene emission rates but only the temperature dependence of emissions for all other compounds It included a simple canopy radiative transfer model differentiating between the conditions of sunlit and sun-shaded leaves at multiple canopy levels. The current version of the MEGAN model (MEGANv2.1) described in Guenther et al (2012) updates the model approach and parameterizations of MEGANv2.02 It calculates the net primary emission of 19 compound classes which are decomposed into 147 individual species such as isoprene, monoterpene and sesquiterpene compounds, carbon monoxide, methanol, alkanes, alkenes, aldehydes, acids, ketones and other oxygenated VOCs. Using the MEGAN postprocessing tool, the species can be lumped into the compound groups of common chemical mechanisms for use in.
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