HAZARDOUS_AIR_POLLUTANTS - 30 September 2008 Version 4.7 of CMAQ contains two mechanisms to simulate the atmospheric fate and transport of mercury compounds and several other Hazardous Air Pollutants (HAPs). One mechanism called SAPRC99TX3_AE5_AQ simulates only the HAPs in CMAQ version 4.6. The other mechanism simulates both mercury compounds and other HAPs and is called CBO5TXHG_AE5_AQ or the Multiple Pollutant mechanism. Building CMAQ with these mechanisms required modified versions of the new photchemistry, aerosol, cloud, and vertical diffusion options in CMAQ version 4.7. The information below describes how CMAQ with the SAPRC99TX3_AE5_AQ mechanism simulates HAPs. See the Multi-Pollutant release notes for information on the CBO5TXHG_AE5_AQ mechanism. In CMAQ using the SAPRC99TX3_AE5_AQ mechanism, a HAP's phase, i.e., gas or aerosol, determines the chemical and physical processes that they undergo. Each HAPs is transported and deposited. 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. In version 4.7, five HAPs in the NR species have explicitly calculated velocities. Their values are calculated within simulations if the model is compiled the acm2_inline_txhg option and if the environment variable, CTM_ILDEPV, is set to T (true) or Y (yes). MCIP version 3.4 also provides the velocities in the METCRO2D files when the MCIP is run calculates maximum number of deposition velocities. Two methods compute the chemical transformation of gas phase HAPs (Table 1). 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) describes 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. Formaldehyde, acetaldehyde, benzene, acrolein and 1,3- butadiene 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 2) 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. Building CCTM with the SAPRC99_AE5_AQ mechanism requires several different build settings than the standard version of CCTM. Table 3 shows the build settings needed to construct CCTM using this mechanism with its EBI solver. Build settings not specified in Table 3 remain the same as the standard CCTM with aerosols. NOTE that the smvgear and ros3 options for the chem module does work for the SAPRC99TX3_AE5_AQ mechanism. 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 SAPRC99 mechanism. 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 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. 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 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 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 BENZENE BENZENE 71-43-2 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 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 2 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 3. Option setting 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_ae5_aq #VDIFF has two possible seeting set ModVdiff = ( module acm2_txhg $Revision; ) # OR though in standard CCTM setting set ModVdiff = ( module acm2_inline_txhg $Revision; ) # Select correct EBI solver # NOTE THAT ros3 and smvgear options also work # # set ModChem = ( module ebi_saprc99tx3_ae5 $Revision; ) #AERO option required set ModAero = ( module aero5_txhg $Revision; ) #cloud processing and aqueous chemistry option required for both #mechanism set ModCloud = ( module cloud_acm2_ae5_tx $Revision; ) =====================================================================