RELEASE NOTES for CAMx v6.20, 03/23/15

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


Overview of Version 6.20
------------------------

V6.20 includes new features, modifications, and bug fixes from the previous
release (v6.10).

* Use the chemistry parameters files specifically labeled for v6.20.
* There are no changes to I/O file formats from v6.10 -- a new optional top
  boundary concentration file has been added.
* The CAMx control file namelist has changed to support certain modifications.
* There are no changes to the way the CAMx makefile is run.


v6.20 Major Updates and New Capabilities
----------------------------------------

1. Added a hybrid 1.5-dimensional (1.5-D) Volatility Basis Set (VBS) approach
   for secondary organic aerosols.

   Implications: The 1.5D VBS is implemented to provide a unified framework for
                 gas-aerosol partitioning and chemical aging of both primary and
                 secondary organic aerosols. The original Secondary Organic 
                 Aerosol Partitioning (SOAP) treatment remains an option, and 
                 has been updated to include SOA from benzene in parallel with 
                 VBS. VBS is compatible only with the 2-mode CF aerosol option;
                 it is not currently enabled for Probing Tools or for the 
                 sectional CMU aerosol option. Chemistry parameters files 
                 enabling VBS are provided for chemistry Mechanisms 2 (CB6r2)
                 and 6 (CB05).

2. Added a new optional top boundary condition input file.

   Implications: A time/space-variable top concentration BC file can be derived
                 from three-dimensional output from global models to improve the
                 characterization of chemicals entering the model top, which is
                 particularly important for common stratospheric constituents 
                 such as ozone and nitrogen oxides. Currently, the GEOS2CAMx 
                 pre-processor is able to generate top boundary conditions from
                 the output of the GEOS-Chem global model. The original internal
                 top boundary treatment remains available, which is the default
                 selection if a top boundary condition file is not explicitly 
                 provided to CAMx in the namelist input file.

3. Added halogen chemistry to CB6 (Mechanism 3, CB6r2h).

   Implications: The CB6r2 mechanism was supplemented with additional reactions
                 involving ocean-borne halogen compounds. Mechanism 3 adds 
                 reactions involving bromine, iodine, and chlorine, with rate 
                 constants updated to currently accepted values and mechanism 
                 revisions to promote consistency. Currently, Mechanism 3 is 
                 not linked to PM chemistry. Previous halogen mechanisms and CB6
                 versions prior to CB6r2 have been removed.


v6.20 Modifications
-------------------

1. Added key chemical process analysis (CPA) variables to CB6r2 (Mechanism 2)

   Implications: Mechanism 2 now includes a few specific CPA tracking variables
                 that are the most important and commonly analyzed rates. A full
                 implementation of CPA for CB6r2 may be considered in the
                 future.

2. Modified PiG puff transport to include explicit vertical velocity to
   account for influences from resolved small scale terrain.

   Implications: This update was developed to result in more realistic plume 
                 effects on surface concentrations in high-resolution complex
                 terrain applications (e.g., plume impingement on small-scale
                 ridges).

3. Certain gas species properties have been updated.

   Implications: Molecular weights and lower bound concentration values have
                 been updated for some gas species.  Expect very minor impacts
                 to concentration and deposition results. Use the chemistry 
                 parameters files labelled CAMx6.2.


v6.20 Bug Fixes
---------------

1. PM-DDM bug fixes.

   Implications: Some bugs were identified and fixed that were leading to
                 NaNs and occasional anomalously large sensitivities for PM 
                 components.