Model of Emissions of Gases and Aerosols from Nature (MEGAN)

MEGAN is a modeling system for estimating the net emission of gases and aerosols from terrestrial ecosystems into the atmosphere. Driving variables include landcover, weather, and atmospheric chemical composition. MEGAN is a global model with a base resolution of ~ 1 km and so is suitable for regional and global models. A FORTRAN code is available for generating emission estimates for the CMAQ regional air quality model. The algorithms have also been incorporated as an on-line component in several regional and global chemistry and transport models. Global distributions of landcover variables (Emission Factors, Leaf Area Index, and Plant Functional Types) are available for spatial resolutions ranging from ~ 1 to 100 km and in several formats (ARCGIS, netcdf).

 

It should be noted that running this version of MEGAN requires both access to and knowledge of a Unix operating system and working knowledge of FORTRAN. If you need to regrid the MEGAN input files then you will also need knowledge/access to Python computer language and ESRI ArcMAP software (or some alternative regridding software). Users who have never been exposed to Unix-type operating systems (i.e., if you are only familiar with Windows) unfortunately will find it difficult to run MEGAN. Although you do not need to be a computer programmer to run the model, you should have a basic understanding of computer programming and Unix (i.e., you should know how to unzip/untar files and other basic commands in Unix, install libraries and link files within Unix, and know basic FORTRAN commands such as how to invoke a code). If you need to regrid landcover data then you should also be familiar with (and have access to) ArcMAP or a similar program. In summary, you should have a working knowledge of ArcMap, Unix, FORTRAN, and Python before attempting to use MEGAN. We have listed information and resources at the bottom of this page that we hope will be helpful to those individuals interested in learning more about the tools and programs necessary to run MEGAN.

 

MEGANv2.04 (released October 29, 2007)

User Guides:

1. FORTRAN code User Guide: Describes how to download and run a FORTRAN code that generates biogenic emission estimates for CMAQ.

2. Data Portal User Guide: Describes how to access the code and input data.

 

Landcover datasets that can be used as inputs for the FORTRAN code v2.04. include version 2.0 and version 2.1

 

MEGAN2.1beta

1. MEGAN2.1 User Guide: Describes how to install and run a FORTRAN code that generates biogenic emission estimates for CMAQ or CAMx. Weather and landcover driving variables are also described.

2. MEGAN2.1 code: MEGANv2.1 FORTRAN code.

3. Input variables preprocessor tool: A tool that can be used to generate input files for MEGANv2.1.

4. North America Leaf Area Index (version 2011) input files: 30 arc-second 8-day average LAI input files for North America for years 2003 to 2011 based on NASA MODIS data. Files are in netcdf format with a file naming convention of lainaYYYYDDD.nc where YYYY is year and DDD is day of year.

5. North America Plant Functional Type (version 2011) input files: 30 arc-second (aggregated from 30 m data) PFT (CLM 16 PFT classification system) input file for year 2008. Files are in netcdf format with a file naming convention of pftNNdddYY.nc where NN is CLM PFT number, ddd is description and YY is year (08 for 2008).

6. Global emission factor input files (version 2011): Emission factor input files. Files are in netcdf format with a file naming convention of cccc.nc where cccc is compound class. Note that this file is optional- the alternative is to have MEGAN generate emission factors from PFTs.

7. MEGAN2.1 test case: MEGANv2.1 input and output data for U.S. test case to see if you are able to run MEGAN2.1 correctly.

 

 

MEGAN development and description

·         Duhl, T., A. Guenther and D. Helmig. Estimating urban vegetation cover fraction using Google Earth® images, J. of Land Use Science, doi: 10.1080/1747423X.2011.587207, 2011. MEGAN landcover technique.

 

MEGAN application

·         Chen, J., J. Avise, A. Guenther, C. Wiedinmyer, E. Salathe, R. Jackson and B. Lamb, Future land use and land cover influences on regional biogenic emissions and air quality in the United States, Atmospheric Environment, 43, 5771-5780, 2009.

·         Chen, J., J. Avise, B. Lamb, E. Salathe, C. Mass, A. Guenther, C. Wiedinmyer, J.-F. Lamarque, S. O’Neill, D. McKenzie, and N. Larkin, The effects of global changes upon regional ozone pollution in the United States, Atmos. Chem. Phys., 9, 1125-1141, 2009.

·         Stavrakou, T., J.-F. Muller, I. De Smedt, M. van Roozendael, . van der Werf, L. Giglio, and A. Guenther, Evaluating the performance of pyrogenic and biogenic emission inventories against one decade of space-based formaldehyde columns, Atmos. Chem. Phys., 9, 1037-1060, 2009.

·         Wang, X., F. Chen, C. Wiedinmyer, A. Guenther, M. Tewari and Z. Chai, Impacts of weather conditions modified by urban expansion on surface ozone: Comparison between the Pearl River Delta and Yangtze River Delta regions, Advances in Atmospheric Sciences, 26, 962-972, 2009.

·         Müller, J.-F., T. Stavrakou, S. Wallens, I. De Smedt, M. Van Roozendael, M. J. Potosnak, J. Rinne, B. Munger, A. Goldstein, and A. B. Guenther , Global isoprene emissions estimated using MEGAN, ECMWF analyses and a detailed canopy environment model, Atmos. Chem. Phys., 8, 1329-1341, 2008.

 

 

 

Contact:

Xiaoyan Jiang <xjiang@ucar.edu>

Alex Guenther <guenther@ucar.edu>

 

Resources for using MEGAN:

FORTRAN is a general purpose language mainly developed to perform mathematical operations, (compilers may be found at http://www.fortran.com/compilers.html), while Python (http://python.org/) is a general-purpose, high-level language. ArcMAP is a Geographic Information System (GIS) software platform that is used (in the case of MEGAN processing) for the input data preprocessing steps (specifically to average the various input dataset values within each cell of your model domain), and is not needed if a user is programming-savvy enough to write spatial allocation code that can perform the same task without ArcMAP. You can find out more about ArcMAP, including how to download a 60-day trial version at: http://www.esri.com/software/arcgis/arcgis-for-desktop/index.html. It is possible that the free trial version of ArcMAP does not include some of the processing tools needed to complete MEGAN input data preprocessing, but is at least a starting point for becoming familiar with ArcMAP.

 

You may also find the following online tutorials useful:

1. FORTRAN tutorial: http://folk.uio.no/steikr/doc/f77/tutorial/index.html

2. UNIX tutorial: http://www.ee.surrey.ac.uk/Teaching/Unix/

3. ArcMAP tutorial (version 9.3): http://webhelp.esri.com/arcgisdesktop/9.3/tutorials/tutorials.htm

4. Python tutorials: http://python.org/