GAMMA model: recent developments

You may already be familiar with the McNeill Group photochemical box model, GAMMA (Gas-Aerosol Model for Mechanism Analysis). GAMMA features detailed, coupled gas- and aqueous aerosol-phase chemistry. We and others use it as a tool to analyze laboratory data and simulate aerosol and cloud chemistry under ambient conditions, including aqueous organic aerosol chemistry in the Southeastern U.S., cloudwater chemistry at Whiteface Mountain, and aerosol-phase sulfate formation in Beijing.

GAMMA was originally designed with a focus on secondary organic aerosol (SOA) and organosulfate formation in the aqueous aerosol phase (McNeill et al., 2012). Since then, the model has also been applied to study inorganic aqueous chemistry in aerosols and aqueous chemistry, including SOA formation, in cloudwater.  A reduced version of the model, simpleGAMMA (Woo and McNeill, 2015) was developed for coupling with large-scale models or for analysis of field data (Budisulistiorini et al., 2015, 2017). GAMMA has also been used to develop parameterizations of aqueous atmospheric chemistry for use in global models (Curry et al., 2018).

The original chemical mechanism and governing equations of GAMMA 1.0 are described in McNeill et al., (2012). A complete listing of the gas and aqueous phase chemical mechanisms and parameters in the original model can be found in the supporting information here.  Development of the GAMMA mechanism is an active area of research for our group. The model is continuously being updated and expanded. Recent updates and additions included in GAMMA 5.0:

  • Expanded and updated gas phase chemistry (C1-C3)
  • Detailed S(IV) to S(VI) (sulfate formation) chemistry
  • Transition metal ion chemistry: Fenton, Clustering, sulfate formation
  • Photosensitizer chemistry (e.g. Tsui et al. 2017, Tsui and McNeill 2018)
  • Reactive uptake option
  • Aqueous-phase reactions of IEPOX with NH4+, and updated IEPOX Henry’s Law constant (Budisulistiorini et al. 2015)
  • Detailed H+ kinetics/Online thermodynamics (ISORROPIA/ISOCALL)
  • Salting effects for glyoxal (Curry et al. 2018)

Some of these features are optional, depending on the application.

For more about the GAMMA and simpleGAMMA models: