Global data has been extracted from the GEOS-Chem chemical transport model run configuration that includes halogens (Cl, Br, I) at 4x5 degree resolution as described in Sherwen et al. (2016). 2x2.5 output is also hosted here.

The data is provided as a NetCDF file that contains gridded output with four dimensions (time, longitude, latitude, model level). The file contains monthly resolution data for one year, starting on January 1st 2005. Monthly average fields for tracers are provided. Coordinates are provided to allow calculation of altitude etc/conversion of units. 


Reference:
T. Sherwen, J.A. Schmidt, M.J. Evans, L.J. Carpenter, K. Großmann, S.D. Eastham, D.J. Jacob, B. Dix, T.K. Koenig, R. Sinreich, I. Ortega, R. Volkamer, A. Saiz-Lopez, C. Prados-Roman, A.S. Mahajan, C. Ordóñez, “Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem”, 2016, Atmospheric Chemistry & Physics, 16, 12239-12271 


Diagnostics:
The diagnostics outputted are documented in detail via the GEOS-Chem manual (http://acmg.seas.harvard.edu/geos/doc/man/appendix_5.html). The diagnostics included in the file are summarised in the NetCDF metadata and also below:

Average tracer concentrations are provided by variables starting IJ_AVG__??? (where “???” is a tracer name) in units of mixing ratio. Concentrations of OH and HO2 are also included (Variable "CHEM_L_S__HO2” and  "CHEM_L_S__OH”). Please note OH concentration is given in molecules/cm3. Please also note that tracer “CH3IT” is methyl iodide. 

For unit conversion etc. molecule density (“BXHGHT_S__N(AIR)”) and mass of air (“BXHGHT_S__AD”) within grid boxes are also provided. 

Three variables are provided as definition of the troposphere. These give the troposphere in terms of hight ("TR_PAUSE__TP_HGHT"), model level (“TR_PAUSE__TP_LEVEL”), and pressure ("TR_PAUSE__TP_PRESS"). 


Coordinates:
The surface grid is given by “longitude“ and “latitude” variables. The vertical boxes are numbered vertically as given by “model_level_number”.

A variable for altitude of a grid box’s bottom edge is provided via conversion of surface pressure in hPa to metres (“BOX_ALT”). The variables for grid box vertical extent (“BXHGHT_S__BXHEIGHT”) and box surface area (“DXYP__DXYP”) have to allow for calculation of volume/altitudes. The surface pressure of each box has also been provided (“PEDGE_S__PSURF”). 


Contact:
If you have any questions about this output please contact Tomas Sherwen (tomas.sherwen@york.ac.uk) or Mat Evans (mat.evans@york.ac.uk).