CHLORINE_CHEMISTRY_NOTES - 15 Sep 2005


 This release contains gas-phase chlorine chemistry in the CMAQ Chemical 
 Transport Model (CCTM). The purpose of these notes is to describe the 
 chlorine mechanism used in the CCTM.

 A chlorine chemical mechanism has been added to the CCTM based on Tanaka 
 et al. (2003). The original chlorine mechanism proposed by Tanaka et al. 
 (2003) contains 13 reactions. However, two of those reactions involve 1,3 
 butadiene and its reaction product. Since the base CB-IV mechanism does 
 not contain 1,3 butadiene, these two reactions were eleminated and the 
 remaining 11 reactions were combined with the CB-IV mechanism and 
 incorporated into the CCTM. An EBI solver has also been developed for the 
 combined mechanism (chlorine + CB-IV mechanism). The current chlorine 
 chemistry can not be used in conjuction with the SAPRC-99 mechanism.

 In-house tests were conducted using chlorine emissions for two cases 
 (Sarwar and Gipson, 2005) (1) In one case, the CCTM was run with molecular 
 chlorine emissions from the 1999 National Emissions Inventory of Hazardous 
 Air Pollutants (2) in the other case, the molecular chlorine was 
 supplemented with HOCl emissions estimated from swimming pools and cooling 
 towers. Initial test results indicate that when molecular chlorine 
 emissions were included in the model, the only impact occurred near the 
 Great Salt Lake. Ozone concentration at that location increased by a 
 maximum of 14 ppbv. When both molecular chlorine and hypochlorous acid 
 emissions were included in the model, the impacts were evident at several 
 areas, including the Great Salt Lake and the Houston area.

 1) Build script for the CMAQ Model with chlorine chemistry:

    Build script distributed with the standard CMAQ model can be used to 
    extract source codes for the chlorine chemistry and the relevant ebi 
    solver. However, the script needs the folowing changes in order to 
    extract the correct files:

    Need to use "ebi_cb4cl" to extract ebi solver source code for the 
    chlorine chemistry:

       set ModChem   = ( module ebi_cb4cl          $Revision; )

    Need to use "cb4cl_ae3_aq" to extract source code for the combined 
    chemistry (CB-IV + Chlorine chemistry):

       set Mechanism = cb4cl_ae3_aq

    The source code can be complied using the modified build script.

 2) Running the CMAQ Model with Chlorine Chemistry:

    The run script distributed with the standard CMAQ model can be used to 
    run the CMAQ model with the chlorine chemistry. However, several 
    additional steps are necessary for running the CMAQ model with chlorine 
    chemistry: 

    The Meteorology Chemistry Interface Processor (MCIP, version 3.0) is 
    needed to generate deposition velocities for six additional species 
    used in the chlorine chemistry. Deposition velocities for these and 
    other species are stored in METCRO2D file generated by the MCIP.

    Sparse Matrix Operator Kernel Emissions (SMOKE) System is needed to 
    generate model-ready chlorine emissions. These emissions need to be 
    added to the files containing emissions of other species used by the 
    CMAQ model.

    Any IC and BC files for the standard CMAQ model can be used to run the 
    CMAQ model with chlorine chemistry. These IC and BC files currently do 
    not contain any values for the additional species in the chlorine 
    chemistry. Therefore, the minimum default value (10E-30 ppm) will be 
    used for these additional species in the CMAQ model with chlorine 
    chemistry. 

 References:

 Sarwar, G., and G. Gipson. The effect of chlorine emissions on tropospheric
     Ozone in the United States. A&WMA 98th Annual Conference, Minneapolis,
     Minnesota, June 21-24, 2005.  Session AB-3c, Development and
     Application of Regional Transport One-Atmosphere Models in a
     Regulatory Context. Air & Waste Management Association, Pittsburgh,
     Paper # 596, 2005.

 Tanaka, P. L., D.T. Allen, E.C. McDonald-Buller, S. Chang, Y. Kimura, C.B.
     Mullins, G. Yarwood, and J.D. Neece, Development of a chlorine
     mechanism for use in the carbon bond IV chemistry model, Journal of
     Geophysical Research, 108(D4), 4145, doi:10.1029/2002JD002432, 2003.