Document ID: EPA-HQ-OAR-2016-0751-0003
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2017-01-06T05:00Z

RELEASE NOTES for CAMx v6.30, 04/08/16

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

Overview of Version 6.30
------------------------

V6.30 includes new features, modifications, and bug fixes from the previous
release (v6.20).

* Use the chemistry parameters files specifically labeled for v6.30. New files
  are available for Mechansims 4 (CB6r3) and 5 (SAPRC07TC).
* A new version of TUV is available to support SAPRC07TC.
* The 2D time-variant met file has changed to include new snow cover variables.
  CAMx remains backward compatible with the original snow cover input.
* A new source apportionment region map file format supports fractional region
  definitions per grid cell. CAMx remains backward compatible with the original
  region map format.
* The CAMx control file namelist has changed to support certain modifications.
* There are no changes to other I/O file formats from v6.20.
* The CAMx makefile now supports the Gnu Fortran compiler (gfortran).
* The Makefile for 32-bit compilers is no longer supported.

v6.30 New Features and Major Updates
------------------------------------

1. Several modifications were implemented to improve model speed.

   Implications: Our tests without Probing Tools indicate speed increases by
                 15-50%, depending on model configuration (grid number and size,
                 PiG, chemistry mechanism), compiler and chipset. These changes
                 have minimal impacts on concentration results (e.g., ozone
                 differences < 1 ppb).

2. OSAT has been expanded to include a more robust handling of O3-NOy
   interactions and to improve consistency with PSAT nitrate chemistry.

   Implications: OSAT now tracks odd oxygen and nitrogen through NOy chemistry
                 to account for NOx recycling of ozone.  OSAT is now more
                 consistent with the PSAT nitrate treatment.  Many more OSAT
                 tracers are necessary, and this affects memory requirements
                 and model speed.  Expect to see slightly more ozone
                 contributions from long range transport, and commensurately
                 less contributions from local emissions.
           NOTE: With this update, source apportionment is not available for
                 the following chemical mechanisms: 3 (CB6r2h); 5 (SAPRC07TC).

3. CAMx can now run on WRF Mercator and Polar projections.

   Implications: A parallel modification has been made to WRFCAMx (v4.4) to
                 support the new projections. Some namelist variables have
                 changed to support this update and to improve clarity.

4. A new snow albedo treatment has been incorporated based on the WRF/NOAH
   land surface model.

   Implications: Time/space-varying snow albedo is determined based on landuse,
                 snow depth and age.  Modifications have been made to WRFCAMx
                 (v4.4) to read snow variables from WRF and to pass snow depth
                 and age fields to CAMx via the 2-D time-variant input file.
                 TUV includes an update to extend the range of albedo classes.
                 Net surface albedo in snow-covered grid cells can be
                 substantially different from the original constant value of
                 50%, and this can have a large impact on photochemical
                 activity.

5. A new CB6 chemistry mechanism (CB6r3 -- mechanism 4) has been introduced
   that includes a temperature- and pressure-dependent organic nitrate branching
   ratio.

   Implications: This update was found to be important for photochemistry in
                 cold and/or elevated conditions, such as wintertime in the
                 US inter-mountain west. Generally, the effect of this change
                 is to reduce ozone production slightly relative to CB6r2 in
                 cold conditions.  There are no appreciable effects in warm
                 conditions that are more typical of the ozone season.

6. SAPRC07TC has replaced SAPRC99 (mechanism 5).

   Implications: SAPRC07 is a more recent gas-phase chemistry mechanism that
                 has replaced the dated SAPRC99 mechanism.  SAPRC07TC is a
                 variant of SAPRC07 that includes extra model species for toxics
                 and uses numerical expressions of rate constants that are 
                 compatible with the current chemistry mechanism solver.
                 SAPRC07TC is consistent with the version in CMAQ so that 
                 emissions will work in either model.  

v6.30 Modifications
-------------------

1. The VBS organic aerosol option has been updated to add a basis set for
   organics from meat cooking, and to remove the internal allocation of POA
   emissions to individual POA and IVOC basis sets.

   Implications: Use the new VBS emissions preprocessor PREPVBS to develop POA
                 and IVOC emissions for all basis sets.  CAMx will stop with an
                 error message if all needed emissions are not found on the
                 emission input files.  See the User's Guide for more
                 information.

2. Heterogeneous reaction rates have been updated.

   Implications: The rate for N2O5+H2O->HNO3 has been updated, and a new rate
                 calculation has been added for N2O5+HCl->CLN2+HNO3.

3. Source apportionment can now use a new source region map format that supports
   fractional (partial) area assignments for each grid cell.

   Implications: Previously, source region maps simply assigned each grid cell
                 to a single source region.  The addition of an optional
                 partial region map allows the user to define multiple regions
                 to each grid cell by source sector.  See the User's Guide for
                 more information.

4. Updated calculations of PiG dry and wet deposition for source apportionment
   tracers.

   Implications: This change improves upon inconsistencies found in treating
                 dry and wet deposition from PiG puffs and deposition sums of
                 source apportionment tracers.

5. The surface chemistry model has been extended to work with the Zhang dry
   deposition option and a new snow compartment has been added.

   Implications: Surface chemistry is now performed for a third (snow, if
                 present) surface type on top of soil and vegetation.  This
                 update is tied to the snow albedo update.  See the User's 
                 Guide for more information.

6. One of the definitions for the PiG shear flag (SHRFLG=1) has been updated.
   A PiG sampling criterion has changed.

   Implications:  SHRFLG=1 now means puff growth by wind shear is always
                  applied in the boundary layer (not just during neutral/
                  unstable conditions) and never applied above the boundary
                  layer.  PiG puffs are now sampled when puffs extend to within
                  10 m of the surface (rather than simply extending into the
                  surface layer) to remove sensitivity to choice of layer
                  structure.

7. A new user option called "ALLR" has been added to force the model to output
   gridded average concentrations for all species including radicals.

   Implications: The option "ALL" outputs all "state" (transported) species to
                 the average and deposition output files.  "ALLR" includes all
                 radicals on the average concentration output files.

8. New flags have been added to the CAMx control (namelist) file to explicitly
   control the use of source apportionment and DDM point source override at
   runtime.

   Implications: Source apportionment and DDM point source override flags can
                 be set for each stack to specify each stack's region
                 assignment.  These flags are set within the input point source
                 files (a transparent feature), so users' may not know that such
                 flags are set; this can lead to confusing SA or DDM results.
                 The new namelist flags allow the user to explicitly turn the
                 override feature on or off at runtime.  See the User's Guide
                 for more information.
 
9. The Implicit-Explicit Hybrid (IEH) chemistry solver option has been
   removed.

   Implications: IEH has been unnecessary since the introduction of the faster
                 Euler-Backward Iterative (EBI) scheme, which is the default
                 solver. 

10. The source apportionment option "GOAT" has been removed.

   Implications: GOAT was an attribution option developed in early versions of
                 OSAT, and is now considered obsolete.

v6.30 Bug Fixes
---------------

1. Removed "-Mconcur=nonuma" from the PGF90 comiler flag list.

   Implications: This flag causes the model to run much slower (by factors of
                 10 or more) for later versions of PGF90 (v13+).

2. Fixed several MPI bugs found for PiG sampling grids.

   Implications: This bug led to clearly incorrect plume patterns on sampling
                 grids relative to non-MPI simulations.  MPI and non-MPI results
                 are now equivalent.

3. Fixed a bug in the sign of v-component divergence in the calculations of PiG
   puff vertical advection.

   Implications: Minor impacts to puff elevation above ground.

4. Fixed two bugs related to RTRAC species names.

   Implications: A fix to the MPI pass of RTRAC species names resolved 
                 segmentation faults.  Another minor bug was found when 
                 checking attributes for RTCMC species.  Some species types may
                 have been incorrectly assigned, depending on how species were
                 ordered in the RTCMC/IMC chemistry parameters file.  The check
                 has been corrected and is now more robust.

5. Minor bug fix to the zenith angle routine GETZNTH in cases when cos(zenith)
   < -1.

   Implications: The cause for cos(zenith)<-1 remains unknown, but code has
                 been modified to trap this, ensuring -1=<cos(zenith)<=+1.

6. Fixed bug in wet deposition of gas-phase species in cases of rain
   evaporation.  Thanks to Ondrej Vlcek, CHMI.

   Implications: Accumulated masses of certain gas species in precipitation
                 could occasionally become slightly negative, resulting in small
                 negative gas concentrations in cases when rain evaporates
                 before reaching the ground (a problem trapped by a check before
                 chemistry).  Accumulated mass is now limited to zero/positive
                 values.