Geosci. Model Dev., 5, 1471–1492, 2012 www.geosci-model-dev.net/5/1471/2012/ doi:10.5194/gmd-5-1471-2012 © Author(s) 2012. CC Attribution 3.0 License. Geoscientific Model Development The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): an extended and updated framework for modeling biogenic emissions A. B. Guenther 1 , X. Jiang 1 , C. L. Heald 2 , T. Sakulyanontvittaya 3 , T. Duhl 1 , L. K. Emmons 1 , and X. Wang 4 1 Atmospheric Chemistry Division, NCAR Earth System Laboratory, Boulder, CO, USA 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA 3 ENVIRON, Novato, CA, USA 4 School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China Correspondence to: A. B. Guenther (guenther@ucar.edu) Received: 9 May 2012 – Published in Geosci. Model Dev. Discuss.: 12 June 2012 Revised: 3 October 2012 – Accepted: 9 October 2012 – Published: 26 November 2012 Abstract. The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1) is a modeling frame- work for estimating fluxes of biogenic compounds be- tween terrestrial ecosystems and the atmosphere using sim- ple mechanistic algorithms to account for the major known processes controlling biogenic emissions. It is available as an offline code and has also been coupled into land surface and atmospheric chemistry models. MEGAN2.1 is an update from the previous versions including MEGAN2.0, which was described for isoprene emissions by Guenther et al. (2006) and MEGAN2.02, which was described for monoterpene and sesquiterpene emissions by Sakulyanontvittaya et al. (2008). Isoprene comprises about half of the total global bio- genic volatile organic compound (BVOC) emission of 1 Pg (1000 Tg or 10 15 g) estimated using MEGAN2.1. Methanol, ethanol, acetaldehyde, acetone, α-pinene, β -pinene, t -β - ocimene, limonene, ethene, and propene together contribute another 30 % of the MEGAN2.1 estimated emission. An additional 20 compounds (mostly terpenoids) are associ- ated with the MEGAN2.1 estimates of another 17 % of the total emission with the remaining 3 % distributed among >100 compounds. Emissions of 41 monoterpenes and 32 sesquiterpenes together comprise about 15 % and 3 %, re- spectively, of the estimated total global BVOC emission. Tropical trees cover about 18 % of the global land surface and are estimated to be responsible for ∼ 80 % of terpenoid emissions and ∼ 50 % of other VOC emissions. Other trees cover about the same area but are estimated to contribute only about 10 % of total emissions. The magnitude of the emissions estimated with MEGAN2.1 are within the range of estimates reported using other approaches and much of the differences between reported values can be attributed to land cover and meteorological driving variables. The of- fline version of MEGAN2.1 source code and driving vari- ables is available from http://bai.acd.ucar.edu/MEGAN/ and the version integrated into the Community Land Model ver- sion 4 (CLM4) can be downloaded from http://www.cesm. ucar.edu/. 1 Introduction Terrestrial ecosystems produce a diverse array of chemi- cals including many volatile and semi-volatile compounds that are emitted into the atmosphere (Goldstein and Gal- bally, 2007). Some of these have an important role in at- mospheric chemistry including reactive volatile organic com- pounds (VOC) for which terrestrial ecosystems are by far the biggest contributors to the global annual flux (Lamarque et al., 2010). It is now widely recognized that these chemicals can influence atmospheric composition and quantitative esti- mates of their emissions into the atmosphere are needed for numerical assessments of past, present and future air qual- ity and climate (e.g., Derwent et al., 2007; Folberth et al., 2006). Isoprene and a few other biogenic VOC (BVOC), in some cases including total monoterpenes, are now routinely Published by Copernicus Publications on behalf of the European Geosciences Union.