RELEASE NOTES for CAMx v7.40, 08/01/26

The Comprehensive Air Quality Model with extensions (CAMx) is available at
www.camx.com.  

Overview of Version 7.40
------------------------

V7.40 includes new features, modifications, and bug fixes from the previous
release (v7.32)

* Use the chemistry parameter files specifically labeled for v7.4.
  We recommend the use of EQSAM over ISORROPIA for inorganic aerosol chemistry.
  Chemistry parameter files have been distributed with EQSAM selected.
* Use the TUV photolysis pre-processor specific to v7.4 that supports CB7r3.
* Check the CAMx control namelist template for the full list of control
  variables specific to this version. Some variables have been removed.
* The operation of the CAMx makefile has not changed since the last version.
  Type "make" or "make help" for more information.
  NOTE: RECENT VERSIONS OF THE GFORTRAN COMPILER WILL NOT COMPILE CAMx
        WITH OMP PARALLELIZATION BECAUSE OF AN INCOMPATIBILITY WITH BLOCK
        DATA IN ISORROPIA. THIS IS NOT AN ISSUE WITH OTHER SUPPORTED COMPILERS.
        OPTIONS:
        a) USE MPI ONLY WITH GFORTRAN
        b) USE A DIFFERENT COMPILER


v7.40 New Features and Major Updates
------------------------------------

1. Carbon Bond version 7, revision 3 (CB7r3) photochemical mechanism.
   * This update adds gas and SOA chemistry related to biomass fires
     (wild, ag, Rx).
   * Includes updates from CB7r2 (not publicly released) that address gas and
     SOA chemistry for volatile consumer products (VCP).
 
   Implications: CB7r3 adds new species related to fire emissions and VCPs,
                 which need to be included in emissions and IC/BC inputs to
                 activate their impact on ozone and PM chemistry (although CB7r3
                 will operate with inputs generated for CB6r4 through CB7r1).
                 CB7r3 replaces CB7r1 and works with all Probing Tools.  Use the
                 TUV photolysis pre-processor specific to v7.4 that supports
                 CB7r3.  See the CAMx User's Guide for more information. 


v7.40 Modifications
-------------------

1. Removed the Plume-in-Grid (PiG) feature.

   Implications: Use of the PiG treatment for point sources is no longer
                 supported in CAMx. PiG was removed to simplify internal point
                 source processing for the core model and Probing Tools, and
                 to remove complications related to plume tracking and mass
                 dumping/sampling across MPI domain slices. The common modern
                 use of higher grid resolution of 1 to 4 km has diminished the
                 original purpose of PiG to resolve near-source non-linear
                 chemistry within plumes traversing coarser grids.

2. Removed legacy binary I/O options.

   Implications: All meteorology, emissions, and initial/boundary condition
                 input files must be in the netCDF format. See the CAMx User's
                 Guide for information on the netCDF input file structures.
                 Conversion tools for legacy binary gridded and point emissions
                 files are posted at www.camx.com.

                 All gridded output files (other than for some PA files) are
                 output in the netCDF format. These formats are compatible with
                 Models-3 software for viewing and manipulating.

3. Improved robustness of RADM aqueous cloud chemistry algorithm (RAQCHEM)

   Implications: Changes include setting bounds for ionic strength, which
                 alleviates occasional model stops due to excessive
                 looping and iterations by the solver. Expect negligible
                 impacts to inorganic PM concentrations generated by the
                 aqueous chemistry pathway.

4. Removed the CB6r4 chemistry mechanism.

   Implications: This mechanism is considered obsolete. Use CB6r5 or CB7.



v7.40 Bug Fixes
---------------

1. Improved processing of primary organic aerosol emissions (POA_XX) into
   evaporated SVOA and remaining POA (HOA) tracers in PSAT. Other updates to
   improve PSAT robustness.

   Implications: PSAT for POA/SVOA/HOA was not correctly tracking source
                 categories.  This fix may substantially alter PSAT results
                 for OA.

2. Miscellaneous minor bug fixes reported by the CAMx user community.