AEROSOL_NOTES - 15 September 2005


1.  AERO4 module.  This aerosol module is new to CMAQ.  It differs from
    AERO3 in one key aspect -- AERO4 contains calculations of sea-salt
    emissions and thermodynamics whereas AERO3 does not. In AERO4,
    emissions of sea salt from the open ocean are calculated as a function
    of wind speed and relative humidity.  These emissions are speciated
    into sodium, chloride, and sulfate, and are distributed by size to the
    accumulation and coarse modes.  All sea-salt emission calculations are
    done within the CMAQ model and do not require any pre-processing in
    SMOKE. However, a new input file called the "OCEANfile" is needed to
    run CMAQ with the AERO4 module.  The OCEANfile is a time-invariant
    IOAPI file that has 1 vertical layer and the same columns and rows as
    the CMAQ domain.  The OCEANfile contains a variable named "OPEN" which
    represents the fraction of each grid cell that is covered by open
    ocean.  An automated procedure for creating an OCEANfile is being
    developed currently that will rely on the Spatial Allocator tool. As an
    interim procedure, users may generate an OCEANfile using the "SSMASK"
    program, which is available at ftp://ftp.epa.gov/amd/asmd/CMAQv4.5/.
    This interim procedure requires a LAND_TOTALS file from BEIS3 to
    generate the OCEANfile.  Full details on how to use the SSMASK program
    are available on the aforementioned ftp site.  Note that sea-salt
    emissions from the surf zone are not treated in the current release,
    and therefore, the OCEANfile need not contain the "SURF" variable.

    Thermodynamic equilibrium between the accumulation-mode (which now 
    includes sodium and chloride) and the gas phase (which now includes 
    hydrochloric acid) are treated within the ISORROPIA equilibrium module. 
    Sea-salt species in the coarse mode are treated as inert tracers. For 
    thermodynamic calculations, hydrochloric acid (HCl) has been added to 
    the nonreactive species list.  The NR_DEPV.EXT include file in all AE4 
    mechanisms contains reference to an explicit deposition velocity for 
    HCl (VD_HCL).  *** Note that this output field is available in MCIP3.0, 
    but not in previous versions of MCIP. ***  The AE_CONC.EXT include file 
    in all AE4 mechanisms does not include species with zero concentrations 
    (i.e. A25I, ANAI, ACLI, AH2OK, ANO3K).

    To use the AERO3 module (i.e., to turn off sea salt), the "ModAero" and 
    the "Mechanism" variables in the bldit script must be changed.  For 
    example, one would change:

        #set ModAero   = ( module aero3              $Revision; )
         set ModAero   = ( module aero4              $Revision; )
    ...
        #set Mechanism = cb4_ae3_aq
         set Mechanism = cb4_ae4_aq
         
    to
    
         set ModAero   = ( module aero3              $Revision; )
        #set ModAero   = ( module aero4              $Revision; )
    ...
         set Mechanism = cb4_ae3_aq
        #set Mechanism = cb4_ae4_aq

    No other changes are required, because all of the other codes are
    backward-compatible.  *** All remaining notes in this file are
    applicable to both AERO3 and AERO4 modules. ***

2.  Aerosol deposition.  There are three updates to the aerosol dry 
    deposition algorithm: a) The impaction term has been replaced with a 
    new form.  b) The impaction process has been restored to the coarse 
    mode. c) The equation for combining turbulent deposition fluxes and 
    gravitational settling has been replaced. These changes are described 
    in more detail in the CMAQv4.5 Science Document.

3.  ISORROPIA.  The aerosol thermodynamic codes are updated to be 
    consistent with ISORROPIA v1.5 (release date: Oct 25, 2003).  In 
    addition, a few bug fixes were made as noted in the in-line 
    documentation of the ISORROPIA-related subprograms. The main effect of 
    these updates is to produce fewer numerical instabilities in the 
    nitrate and ammonium concentrations than are produced using CMAQv4.4.

4.  PM2.5 Size Cut.  A new subroutine has been added to the aerosol module 
    to calculate the volume fraction of each mode that is composed of 
    particles smaller than 2.5um aerodynamic diameter.  These new variables 
    (PM25AT, PM25AC, and PM25CO) are written to the aerosol diagnostic file 
    and facilitate a more rigorous calculation of PM2.5 than a simple 
    summation of Aitken and accumulation modes.  This update follows the 
    recommendations of Weimin Jiang, Steve Smyth, Eric Giroux, Helmut Roth, 
    an Dazhong Yin, from the National Research Council of Canada. To make 
    use of this feature, users must write out the aerosol diagnostic output 
    file by inserting the following lines into the CMAQ run script:
    
        #> aerosol diagnostic file [ T | Y | F | N ]
         setenv CTM_AERDIAG Y

5.  AERO_EMIS bug fix.  The aerosol emission processor has been modified to 
    correctly convert the H2SO4 emissions into particulate sulfate.  A unit 
    conversion error in v4.4 was reported by Jinyou Liang or CARB, and 
    later, by Prakash Karamchandani, Krish Vijayaraghavan, and Christian 
    Seigneur of AER.

6.  Mode crossover.  A bug in the mode-merging section of SUBROUTINE 
    AEROPROC was identified that prevented mode merging in the cases where 
    it was needed most.  The bug was fixed, eliminating the most extreme 
    cases of "mode crossover" (instances where the Aitken mode diameter 
    grew larger than the accumulation mode).  This bug was identified by 
    Chris Nolte of EPA.

7.  ISORROPIA TSO4 input.  The sulfate concentration used as input to 
    ISORROPIA was modified to include the pre-existing sulfate plus the 
    sulfate produced by gas-phase oxidation in the previous time step.  As 
    a result, the inorganic aerosol components printed to the CONC file are 
    in thermodynamic equilibrium with the gas phase at the end of each time 
    step.

8.  Inconsistency in MINL2SG (aerodepv).  The minimum standard deviation 
    for the aerosol size distribution used in SUBROUTINE AERODEPV was 
    changed to be consistent with the value specified in MODULE 
    AERO_INFO_AE3. This problem was reported by Krish Vijayaraghavan of 
    AER.

9.  Sulfate tracking.  A new optional diagnostic model configuration is is 
    included in CMAQv4.5 to explicitly track the separate contributions to 
    sulfate from the gas-phase and five aqueous-phase chemical reactions, 
    as well as contributions from direct emissions and initial and boundary 
    conditions.  Complete details can be found in the file entitled 
    "SULFATE_TRACKING" located within this directory.

10. Carbon source apportionment.  Another new diagnostic model 
    configuration in CMAQv4.5 provides users the option to track the 
    contributions of elemental carbon and primary organic carbon from up to 
    10 different source categories or source regions.  Details can be found 
    in the file entitled "CARBON_APPORTIONMENT" located within this 
    directory.