Submitted as: development and technical paper
10 Feb 2022
Submitted as: development and technical paper | 10 Feb 2022
Status: this preprint is currently under review for the journal GMD.

Comparison and evaluation of updates to WRF-Chem (v3.9) biogenic emissions using MEGAN

Mauro Morichetti1, Sasha Madronich2, Giorgio Passerini3, Umberto Rizza1, Enrico Mancinelli3, Simone Virgili3, and Mary Barth2 Mauro Morichetti et al.
  • 1Institute of Atmospheric Sciences and Climate, National Research Council of Italy, Unit of Lecce, Italy
  • 2National Center for Atmospheric Research, Boulder, Colorado, USA
  • 3Department of Industrial Engineering and Mathematical Science, University of Polytechnic of Marche, Ancona, Italy

Abstract. Natural gases produced by the Earth’s ecosystem include a wide range of volatile compounds such as isoprene, monoterpene, nitric oxide, carbon monoxide, and other non-methane volatile organic compounds: the so-called biogenic volatile organic compounds (BVOCs). BVOCs are highly reactive and thus can impact air quality and aerosol radiative forcing. BVOC emission fluxes have been consistently included in global and regional chemical transport models (e.g., Model of Emissions of Gases and Aerosols from Nature, MEGAN). However, present climate models still have large uncertainties in estimating biogenic trace gases. These uncertainties result from several factors, including uncertainties in emission activity factors that are controlled by environmental conditions, specification of vegetation type, and plant emission factors. This work concerns the evaluation and test of a set of updates made to MEGAN, a model for estimating fluxes of biogenic compounds between terrestrial ecosystem and the atmosphere, which is embedded into the Weather Research and Forecasting model coupled with chemistry (WRF-Chem version 3.9). Two different test cases are presented, the first covering Europe, and the second for a domain in the Southeast United States. Our study considers four simulations for each update made to MEGAN, (i) a control run with no changes to MEGAN; (ii) a simulation with the emission activity factors modified following MEGAN version 2.10; (iii) a simulation considering the changes to the plant functional type emission factor; (iv) a simulation with the isoprene emission factor calculated within the MEGAN module (the emission factor of isoprene is obtained from the input database directly in WRF-Chem). For the Europe domain region, a sensitivity study on BVOC emissions was performed for a high-ozone episode in August 2015. The updated MEGAN model led to significant increases, by factors of 2 or more, of the estimated BVOC emissions. The comparison of WRF-Chem results for the European domain with experimental data from the Airbase web-portal (European air quality database) showed that the temporal and spatial distribution of ozone are well represented. However, comparing the updated MEGAN simulations with the control run, ozone concentration bias increased substantially. Results from the U.S. domain are compared with the Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks (NOMADSS) field campaign data (June 2013), which allows for direct comparison of isoprene mixing ratios with observations. The comparison between the modeled data and aircraft observations shows that isoprene mixing ratios agree well with measured isoprene for the M2.04 simulation but are overpredicted considerably by the M2.10 simulation.

Mauro Morichetti et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-15', Anonymous Referee #1, 07 Mar 2022
    • AC1: 'Reply on RC1', Mauro Morichetti, 13 May 2022
  • RC2: 'Comment on gmd-2022-15', Anonymous Referee #2, 13 Mar 2022
    • AC2: 'Reply on RC2', Mauro Morichetti, 13 May 2022

Mauro Morichetti et al.

Mauro Morichetti et al.


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Short summary
In the present study, we explore the effect of making simple changes to the existing WRF-Chem MEGAN v2.04 emissions to provide MEGAN updates that can be used independently of land surface model chosen. In the present study, the changes made to the MEGAN algorithm implemented in WRF-Chem were the following: (i) update of the emission activity factors, (ii) update of emission factor values for each plant functional type (PFT), and (iii) the assignment of the emission factor by PFT to isoprene.