HAZARDOUS_AIR_POLLUTANTS - 29 Sep 2006 Version 4.6 of CMAQ introduces two new mechanisms to simulate the atmospheric fate and transport of several Hazardous Air Pollutants (HAPs). Each mechanism simulates the HAPs in CMAQ version 4.5. They also simulate a greater number of gas phase HAPs as well as several toxic metals and diesel components in particulate material. One mechanism, called SAPRC99TX3, extends the version 4.5 of SAPRC99 (Carter, 2000a and 2000b) for HAPs. The other, called CB05CLTX, adapts the Carbon Bond 05 (CB05) mechanism released in version 4.6 (Sarwar et al. 2006 and Yarwood et al. 2005). While using the above mechanisms, the chemical transport model treats HAPs based on their phase. All undergo transport and deposition. Wet deposition is determined by the Henry's Law Constant or scavenging rate of the aerosol mode. Aerosol mode also determines dry deposition velocity for aerosol phase pollutants. For the gas phase HAPS, dry deposition has a nonzero velocity if the EPI Suite program (USEPA, 2005) and the SPECTRUM Laboratory database (http://www.speclab.com/price.htm) indicate dry deposition as a fate determining process. Check the NR_DEPV.EXT and GC_DEPV.EXT files for which gas phase HAPs undergo dry deposition. Two methods compute the chemical transformation of gas phase HAPs (Tables 1 and 2). The first is done within the standard numerical solver for ozone and radical chemistry such as the Euler Backward Iterative solver (Hertel et al., 1993). The chemical reactions are listed in the mech.def file. The method may affect the solution for ozone and radical concentrations if the pollutant has high enough concentrations. The second method estimates loss from chemical reactions based on the solution from ozone and radical chemistry and does not alter the ozone and radical concentrations. Luecken et al. (2006) and the release notes for CMAQ version 4.5 describe the approach. The first method mentioned above treats two types of model species. Type one destroys and produces model species influencing ozone and radical concentrations. In CB05CLTX, formaldehyde and acetaldehyde belong to type one. In SAPRC99TX3, acrolein and 1,3-butadiene also belong to type one. Type two does not alter ozone and radical concentrations and serves as tracers of emitted pollutants. Tracers for formaldehyde, acetaldehyde and acrolein emissions allow determining photochemical production of the given pollutant. Aerosol phase HAPs (Table 3) use a modeling approach analogous to tracers in the gas phase. They track emissions of toxic components within PM and undergo microphysical processes and deposition similar to elemental carbon and unidentified coarse mode matter. However, the HAP species do not affect rates of microphysical processes and deposition due to their tracking function. They also do not participate in cloud chemistry. The approach is not valid for two toxic components in PM. Research (Kotas and Stasicka 2000, Zhang 2000 and Seigneur and Constantinou 1995) indicates that hexavalent and trivalent states of chromium exchange mass through chemistry within cloud droplets. Removing this shortcoming is an avenue for future research for model developers within CMAS. CB05CLTX contains additional species (Table 4) and reactions not included in SAPRC99TX3. Six species track emissions from anthropogenic and biogenic sources. Other species allow simulating the fate and transport of molecular chlorine and hydrogen chloride emissions. The additional reactions not only simulate the photochemical destruction of these eight compounds but also simulate how the chlorine compounds affect ozone photochemistry. To simulate the effect, CB05CLTX includes species representing the daughter products of molecular chlorine and hydrogen chloride. Except for one reaction involving hydrogen chloride, Yarwood et al. (2005) recommended the reactions for chlorine compounds based on Tanaka et al. (2003). We added a reaction between hydrogen chloride and the hydroxyl radical (Bryukov et al., 2006) to better simulate the fate of the former compound. CURRENTLY, THE CB05CLTX MECHANISM OMITS MOLECULAR CHLORINE AND HYDROGEN CHLORIDE EMISSIONS BY MULTIPLYING THEIR EMISSIONS WITH ZERO. IF A USER WISHES TO INCLUDE THE EMISSIONS, THEY NEED TO MODIFY THE GC_EMIS.EXT FILE. Building CCTM with the new mechanisms requires use of several different module options than the standard version of CCTM. Table 5 shows the build script options needed to construct CCTM using a HAP mechanism with its EBI solver. Options not specified in Table 5 remain the same as the standard CCTM with aerosols. NOTE that the smvgear and ros3 options for the chem module work with both CB05CLTX and SAPRC99TX3 mechanisms. NOTE: You must use the I/O API version 3.1beta or newer to support the larger number of variables required by the Multipollutant version of CMAQ. To run these CCTM versions, the user needs emissions files containing rates listed in the GC_EMIS.EXT, NR_EMIS.EXT and AE_EMIS.EXT files. The files contain emissions that are not identical to the original CB05 and SAPRC99 mechanisms. A user must complete SMOKE processing with correct ancillary files and the merged NEI/Toxics database. To obtain these items contact the CMAS Help desk at www.cmascenter.org. References Bryukov, M. G., B. Dellinger and V. D. Knyazev, 2006. Kinetics of the gas- phase reaction of OH with HCl. Journal of Physical Chemistry A, 110, 936- 943. Carter, W.P.L., 2000a. "Implementation of the SAPRC-99 Chemical Mechanism into the Models-3 Framework," Report to the United States Environmental Protection Agency, January 29. Available at http://www.cert.ucr.edu/~carter/absts.htm#s99mod3. Carter, W.P.L., 2000b. Documentation of the SAPRC 99 Chemical Mechanism for VOC Reactivity Assessment. Final Report to California Air Resources Board Contract No. 92 329, and 95 308. May, 2000. Available at http://pah.cert.ucr.edu/~carter/absts.htm#saprc99 Hertel, O., R. Berkowicz and J. C. Hov, 1993. Test of two numerical schemes for use in atmospheric transport-chemistry models. Atmospheric Environment, 27, 2591-2611. Kotas, J and Z. Stasicka, 2000. Chromium occurrence in the environment and methods of its speciation. Environmental Pollution, 107, 263-283. Luecken, D. J., W. T. Hutzell and G. L. Gipson 2006. Development and analysis of air quality modeling simulations for hazardous air pollutants. Atmospheric Environment, 40, 5087-5096. Seigneur, C. and E. Constantinou, 1995. Chemical kinetics mechanism for atmospheric chromium. Environmental Science and Technology, 29, 222-231. Sarwar, G., D. Luecken, G. Yarwood, G. Whitten, and W.P.L. Carter, 2006. Impact of an Updated Carbon Bond Mechanism on Predictions from the Community Multiscale Air Quality Model, submitted to the Journal of Applied Meteorology and Climatology. US Environmental Protection Agency, cited 2005. Estimations Programs Interface for Windows (EIPWIN), version 3.12. Available online at http://www.epa.gov/opptintr/exposure/pubs/episuitedl.htm Tanaka P.L., D.T. Allen, E.C. McDonald-Buller, S. Chang, Y. Kimura, G. Yarwood and J.D. Neece, 2003. Development of a chlorine mechanism for use in the carbon bond IV chemistry model. Journal of Geophysical Research, 108, 4145. Yarwood, G., S. Rao, M. Yocke, and G.Z. Whitten, 2005. Updates to the Carbon Bond Mechanism: CB05. Report to the U.S. Environmental Protection Agency, RT-04-00675. Available online at http://www.camx.com/publ/pdfs/CB05_Final_Report_120805.pdf. Zhang, H., 2000. Light and Iron(III)-induced oxidation of chromium(III) in the presence of organic acids and manganese(II) in simulated atmospheric water. Atmospheric Environment, 34, 1633-1640. Table 1 Gas Phase HAP Species in CB05CLTX ============================================================================= Species Name Compound CAS# In mech.def file ============================================================================= FORM total FORMALDEHYDE 50-00-0 Yes ALD2 total ACETALDEHYDE 75-07-0 Yes ACROLEIN total ACROLEIN 107-02-8 Yes BUTADIENE13 1,3-BUTADIENE 106-99-0 Yes FORM_PRIMARY FORMALDEHYDE emissions 50-00-0 Yes ALD2_PRIMARY ACETALDEHYDE emissions 75-07-0 Yes ACROLEIN_PRIMARY ACROLEIN emissions 107-02-8 Yes ACRYLONITRILE ACRYLONITRILE 107-13-1 No CARBONTET CARBON TETRACHLORIDE 56-23-5 No PROPDICHLORIDE PROPYLENE DICHLORIDE 78-87-5 No DICHLOROPROPENE 1,3-DICHLOROPROPENE 542-75-6 No CL4_ETHANE1122 1,1,2,2TETRACHLOROETHANE 79-34-5 No BENZENE BENZENE 71-43-2 No CHCL3 CHLOROFORM 67-66-3 No BR2_C2_12 1,2DIBROMOETHANE 106-93-4 No CL2_C2_12 1,2DICHLOROETHANE 107-06-2 No ETOX ETHYLENE OXIDE 75-21-8 No CL2_ME METHYLENE CHLORIDE 75-09-2 No CL4_ETHE PERCHLOROETHYLENE 127-18-4 No CL3_ETHE TRICHLOROETHYLENE 79-01-6 No CL_ETHE VINYL CHLORIDE 7501-4 No NAPHTHALENE NAPHTHALENE 91-20-3 No QUINOLINE QUINOLINE 91-22-5 No HYDRAZINE Hydrazine 302-01-2 No TOL_DIIS 2,4-Toluene Diisocyanate 584-84-9 No HEXAMETHY_DIIS Hexamethylene 1,6-Diisocyanate 822-06-0 No MAL_ANHYDRIDE Maleic Anhydride 108-31-6 No TRIETHYLAMINE Triethylamine 121-44-8 No DICHLOROBENZENE 1,4-Dichlorobenzene 106-46-7 No ============================================================================= Table 2 Gas Phase HAP species in SAPRC99TX3 ============================================================================= Species Name Compound CAS# In mech.def file ============================================================================= HCHO*see below total FORMALDEHYDE 50-00-0 Yes CCHO total ACETALDEHYDE 75-07-0 Yes ACROLEIN ACROLEIN 107-02-8 Yes BUTADIENE13 1,3-BUTADIENE 106-99-0 Yes FORM_PRIMARY FORMALDEHYDE emissions 50-00-0 Yes ALD2_PRIMARY ACETALDEHYDE emissions 75-07-0 Yes ACROLEIN_PRIMARY ACROLEIN emissions 107-02-8 Yes ACRYLONITRILE ACRYLONITRILE 107-13-1 No CARBONTET CARBON TETRACHLORIDE 56-23-5 No PROPDICHLORIDE PROPYLENE DICHLORIDE 78-87-5 No DICHLOROPROPENE 1,3-DICHLOROPROPENE 542-75-6 No CL4_ETHANE1122 1,1,2,2TETRACHLOROETHANE 79-34-5 No BENZENE BENZENE 71-43-2 No CHCL3 CHLOROFORM 67-66-3 No BR2_C2_12 1,2DIBROMOETHANE 106-93-4 No CL2_C2_12 1,2DICHLOROETHANE 107-06-2 No ETOX ETHYLENE OXIDE 75-21-8 No CL2_ME METHYLENE CHLORIDE 75-09-2 No CL4_ETHE PERCHLOROETHYLENE 127-18-4 No CL3_ETHE TRICHLOROETHYLENE 79-01-6 No CL_ETHE VINYL CHLORIDE 7501-4 No NAPHTHALENE NAPHTHALENE 91-20-3 No QUINOLINE QUINOLINE 91-22-5 No HYDRAZINE Hydrazine 302-01-2 No TOL_DIIS 2,4-Toluene Diisocyanate 584-84-9 No HEXAMETHY_DIIS Hexamethylene 1,6-Diisocyanate 822-06-0 No MAL_ANHYDRIDE Maleic Anhydride 108-31-6 No TRIETHYLAMINE Triethylamine 121-44-8 No DICHLOROBENZENE 1,4-Dichlorobenzene 106-46-7 No ============================================================================= *Note that HCHO is an explicit species in the original SAPRC99 and may not be considered a new species in SAPRC99TX3. Table 3 Aerosol Phase HAP species in CB05CLTX and SAPRC99TX3 (Note that species exist in each aerosol mode) =============================================================================== String in Aerosol Species Represents =============================================================================== BE Beryllium Compounds NI Nickel Compounds CR_III Chromium (III) Compounds CR_VI Chromium (VI) Compounds PB Lead Compounds MN Manganese Compounds CD Cadmium Compounds DIESEL Diesel Emissions =============================================================================== Table 4 Additional Gas Phase Species in CB05CLTX ============================================================================= Species Name Compound CAS# In mech.def file ============================================================================= TOLU Toluene Emissions 108-88-3 YES MXYL M-Xylene Emissions 108-38-3 YES OXYL O-Xylene Emissions 95-47-6 YES PXYL P-Xylene Emissions 106-42-3 YES APIN Alpha-Pinene Emissions 80-56-8 YES BPIN Beta-Pinene Emissions 127-91-3 YES CL2 Molecular Chlorine 7782-50-5 YES HCL Hydrogen Chloride 7647-01-0 YES HOCL Hypochlorous acid 7790-92-3 YES CL Atomic Chlorine 22537-15-1 YES CLO Chlorine Oxide 14989-30-1 YES FMCL Formyl Chloride 2565-30-2 YES ============================================================================= Table 5. Options needed in CCTM build script if using EBI solver. NOTE that unspecific options remain same as CCTM with aerosols. _______________________________________________________________________________ #Select a HAP mechanism set Mechanism = saprc99tx3_ae4_aq # or set Mechanism = cb05cltx_ae4_aq #VDIFF options required for both HAP mechanisms set ModVdiff = ( module acm2_tx $Revision; ) # OR though option not in standard CCTM set ModVdiff = ( module eddy_tx $Revision; ) # Select correct EBI solver for HAP mechanism # NOTE THAT ros3 and smvgear options work with both HAP mechanisms # #if saprc99tx3_ae4_aq # set ModChem = ( module ebi_saprc99tx3 $Revision; ) #if cb05cltx_ae4_aq set ModChem = ( module ebi_cb05cltx $Revision; ) #AERO option required for both HAP mechanisms set ModAero = ( module aero4_tx $Revision; ) #cloud processing and aqueous chemistry options required for both mechanisms set ModCloud = ( module cloud_acm_tx $Revision; ) # OR though option not standard CCTM set ModCloud = ( module cloud_radm_tx $Revision; ) _______________________________________________________________________________