CMAQ version 5.1 (September 2015 beta release) Technical Documentation

Release Notes for CMAQv5.1beta - September 2015

The Community Multiscale Air Quality (CMAQ) modeling system Version 5.1 (CMAQv5.1) is scheduled for release in September 2015. To facilitate community contributions to this model release, a “Beta” version was created and made available to external collaborators/developers on April 10, 2015. There are several new features included in this release (see below). This Beta-version will undergo extensive application and evaluation over the next few months, which may lead to additional changes before the final release this fall.

Contact the U.S. EPA Atmospheric Model Development Branch (Jon Pleim - pleim.jon (at) epa.gov ) if you would like to access the beta-version of CMAQv5.1

Changes and new features

Gas and Aerosol Chemistry

• Simultaneous solution of gas and heterogeneous chemical reactions
• Updates to the CB05 (CB05e51) gas-phase mechanism
  • Updated photolysis cross sections and quantum yields
  • Improved representation of organic nitrogen reaction rates, solubility, products
  • Updated PAN-type compound reaction rates and products
  • Explicit acrolein, 1,3-butadiene, naphthalene, and additional isoprene products
  • Added OH yield from peroxyradical reactions with HO2
  • Updated OH+NO2 reaction rate
  • Additional SOA from PAHs, alkanes, IEPOX, and isoprene+NO3
• Revisions to In-Line Calculations of Photolysis Rates
  • Alternative methods for aerosol optical properties based on Mixing Model and Mie Theory
  • Clouds effects more consistent with cloud model in meteorological model
• Condensed halogen chemistry
• Nitryl chloride chemistry

Emissions/Land Surface

• Updates to sea spray aerosol emissions
  • Updates to emission algorithms (Sea surface temperature dependence)
  • Change in aerosol size distribution
  • Revision in the surf zone emissions
• Updates to Biogenic emissions (BEIS)
  • Two layer canopy model
• Dynamic sunlight and shaded layers
  • Updated the light response function in the canopy model (following Niinemets et al., 2010)
  • New leaf temperature algorithms
  • Updates to Biogenic Emission Landuse Data (BELD) and emission factors
    • Using 2002, 2006, and 2011 National Land Cover Database plant functional types (CONUS) and year specific MODIS plant functional types (global)===
    • 2001 and 2005 USDA Census of Agriculture data
    • USFS Forest Inventory Analysis v5.1 data from 2002-2013
  • Revisions to dry deposition
    • More explicit treatment of organic N deposition species and revisions to Henry's constant
    • Enhanced deposition of O3 over oceans due to the influence of iodide
    • Restructuring of m3dry

Cloud and Aerosol Microphysics

• Aerosol microphysics
  • Nucleation parameterization
    • Vehkamaki et al. (2002) nucleation update
  • Updated modal size fractions for PM emissions (based on Elleman and Covert, 2010)
  • Gravitational settling of coarse aerosols from upper layers