RELEASE NOTES for CAMx v6.40, 12/23/16 The Comprehensive Air Quality Model with extensions (CAMx) is available at http://www.camx.com. Overview of Version 6.40 ------------------------ V6.40 includes new features, modifications, and bug fixes from the previous release (v6.30) * Use the chemistry parameters files specifically labeled for v6.4. New files are available to support several chemistry updates. A new file is available for Mechanism 4 (CB6r4). * The CAMx control namelist file has changed to support certain modifications. * The optional ocean mask (land/water) panel has been removed from the O3MAP file: the distinction between ocean and fresh water is now specified only in the landuse (2-D invariant) input file. * There are no changes to other I/O file formats from v6.30. * The CAMx makefile now supports the option to compile with IEEE math functions to maximize consistency in results between compilers and chipsets. See the README file that comes with the source code, or type "make" or "make help" for more information. v6.40 New Features and Major Updates ------------------------------------ 1. A new CB6 chemistry mechanism (CB6r4 as Mechanism 4) is introduced that combines CB6r3 (previously Mechanism 4) and a condensed halogen mechanism for ocean-borne inorganic reactive iodine (I16B). CB6r4 also adds pseudo- heterogeneous hydrolysis of isoprene-derived organic nitrate (INTR), and a new heterogeneous SO2 oxidation pathway on primary crustal fine PM. Implications: The iodine mechanism is condensed from the full CB6r2 halogen chemistry (Mechanism 3) while maintaining reactions that constitute the three important catalytic cycles of ozone destruction by iodine, as well as the dominant iodine removal reactions. A specialized iterative EBI solver (the IOX solver) was developed for stiff reactions involving iodine species to speed the chemical solution. Ozone impacts are similar to the full halogen mechanism but runtimes are reduced. Expect negligible to minor sulfate impacts in most typical cases; expect larger sulfate impacts during high dust conditions. 2. A new in-line inorganic iodine (Ix) emissions algorithm has been added to support halogen chemistry mechanisms. Implications: This option is controlled by a new CAMx.in namelist variable "Inline_Ix_Emissions". Emissions of Ix from ocean surfaces are dependent on ambient ozone concentrations, wind speed, and SST. Ix emission fluxes are output to the deposition file for diagnostic evaluation and reporting purposes. To avoid double- counting of Ix emissions, the model will stop if it detects I2 and HOI emissions on the input emissions files. 3. Major revision to the SOAP secondary organic aerosol chemistry/partitioning algorithm. The mechanism has been restructured and condensed from 17 to 10 species by removing 3 biogenic CG-SOA pairs and SOAH. The mechanism now includes 4 CG-SOA pairs (2 each for anthropogenic and biogenic), SOPA and SOPB (polymerized non-volatile anthro and bio SOA). Implications: The revision includes updated SOA yields, saturation concentrations, and water solubility parameters. A new aqueous pathway has been added for biogenic SOPB formation from isoprene products glyoxal, methyl glyoxal, and glycolaldehyde. Expect to see higher SOA concentrations with the updated chemistry parameters; you may continue to use SOAP with original chemistry parameters (see chemistry parameters files labelled SOAP and SOAP2). NOTE: These updates have not been extended to DDM yet, so DDM is disengaged for all mechanisms that include PM in this version of CAMx. You may continue to use H/DDM with gas-only mechanisms. 4. Updated aqueous metal-catalyzed and peroxide reactions in the Regional Acid Deposition Model aqueous chemistry algorithm (RADM-AQ). Implications: Mostly minor impacts to sulfate concentrations. Impacts likely moderated by wet deposition updates (see below). 5. Major revision to the wet deposition algorithm. Implications: The algorithm was reviewed in detail to identify assumptions or processes that were unintentionally or otherwise unreasonably limiting gas and PM uptake into precipitation. The wet deposition algorithm was simplified and improved in several ways, resulting in increased scavenging of gases and PM. v6.40 Modifications ------------------- 1. Source apportionment (OSAT/APCA and PSAT) has been updated to account for ozone destruction by iodine and for iodine chemistry impacts on nitrate and isoprene nitrate. PSAT has been updated for the revised SOAP algorithm and the addition of the aqueous biogenic SOA pathway. Effects from heterogeneous SO2 oxidation is handled directly within the gas-phase chemistry portion of PSAT. Implications: SA results will change with these updates. The OSAT update does not change number of tracers, so OSAT runtimes should not be impacted. The SOA update has reduced the number of organic PM tracers, so PSAT for SOA will run faster. 2. The option to provide an ocean mask (aka land/water mask) input has been removed from the O3MAP file and now the distinction between ocean and fresh water bodies is made explicitly in the CAMx input landuse file. Implications: The CAMx landuse file has the capacity to differentiate water type, but typically all water has been assigned to a single land cover category. Now this distinction is necessary to ensure that the in-line Ix emissions are emitted from ocean bodies only. Users should develop landuse fields that explicitly make this distinction. Alternatively, a program called "watermask" should be run on the CAMx landuse file to distribute ocean and fresh water coverages into separate land cover categories. "Watermask" is posted on the downloads page. 3. Implemented the faster ACM2 solver from CMAQ v5.1. Implications: CAMx runtimes with ACM2 invoked are now similar to the default K-theory option. ACM2 has been extended to work with H/DDM sensitivities. 4. The default critical snow SWE values for urban and shrubland landuse categories have been reduced to increase snow cover (and thus albedo) for those areas. Implications: This modification is based on results reported by the Utah DAQ for winter simulations of Salt Lake City. Snow cover and surface albedo will be markedly higher for urban landuse, and moderately higher for shrublands. See the User's Guide for lists of the critical snow SWE by landuse type. 5. Removed SA and DDM output file flags from their respective namelist sections: SA_Master_Sfc_Output SA_Nested_Sfc_Output DDM_Master_Sfc_Output DDM_Nested_Sfc_Output Implications: These flags were unneeded and did not properly control SA and DDM output. SA tracer output files are always generated for all grids and DDM sensitivity output files are generated for specific grids as determined by the DDM_Calc_Grid flag. Old scripts will continue to work correctly if the variables listed above remain in your namelists; they will be ignored. 6. Revised anthropogenic and biogenic classification of VBS SOA precursors. Implications: Classification of VBS SOA precursors are now simplified reflecting the fact that aromatic precursors are mostly anthropogenic and isoprene and terpenes are mostly biogenic. This modification will have no impact on the model results. Users converting the SOAP emissions inputs for VBS using the PREPVBS tool need to use updated PREPVBS. 7. Revised heterogeneous N2O5 uptake rate constant formula to include aerosol size effect. Implications: This should have a very minor impact on the model results. v6.40 Bug Fixes --------------- 1. Bug fix to Zhang aerosol deposition scheme when compiled with IFORT. Implications: Occasional NaNs were generated by the Zhang scheme using the Intel compiler; the reason for this was never clear. The fix is general and robust for all compilers. 2. Bug fix to PiG vertical advection scheme. Implications: NaNs were generated in the rare circumstance when a PiG puff moved to a layer interface where vertical velocity is exactly zero. 3. Bug fix in O/PSAT when specifying only a master grid region map file in a nested grid run. Implications: This bug was introduced with the partial region map option in v6.30. Under conditions described above, grid-total SA emissions were not summed correctly and led to a model stop when they did not agree with core model emission inputs. 4. Bug fix in calculation of DDM sensitivity to top concentrations. The namelist variable "DDM_Top_Concentrations" has been added. Implications: DDM (and HDDM) was not updated for calculating sensitivities to the new optional (time/space-variable) top boundary conditions input file (introduced with CAMx v6.20), which leads to incorrect sensitivities to the top concentrations.