CMAQ Release Notes: Instrumented Models: CMAQ ISAM

Correct ISAM for aerosol sedimentation

William T. Hutzell, U.S. Environmental Protection Agency
Type of update: Science Update
Release Version/Date: CMAQv5.5

Description: Allows the CMAQ ISAM model to account for loss of aerosol mass from gravitational sedimentation.

Significance and Impact: The changes improves ISAM predictions for aerosol contributions for source sectors so the sum over source sectors better agrees with the concentrations. The improvements are strongest for coarse aerosols species that do not have complex aerosol chemistry. Aerosol species representing toxic metals belong to this category. Improvement was also notices in accumulation and coarse modes for sulfate. However, the Normalized Mean Bias shifted from negative to positive in the accumulation modes for toxic metals but remained less than one precent.

Internal PRs: PR#979

ISAM Cloud Processing Update

Sergey L. Napelenok, U.S. Environmental Protection Agency
Type of update: Bug Fix
Release Version/Date: CMAQv5.5
Description: In rare instances, the slight difference in mass between the sum of tags and the corresponding bulk quantity leads to instability in ISAM results. This PR also addresses the zero arrays for the first hour of the ISAM output files.

Significance and Impact: Some instabilities in the ISAM results can manifest as a results of how mass is distributed between tags immediately after cloud chemistry processing. ISAM output files will also have not-zero values during the first output timestep.

References: N/A
Internal PRs: PR#1057

CMAQ-ISAM Bug Fixes to CMAQ-ISAM released with v5.4

Sergey L. Napelenok, U.S. Environmental Protection Agency
Type of update: Bug Fix
Release Version/Date: CMAQv5.5
Description: This update includes several bugfixes:

1. CMAQ-ISAM crashes when compiled in debug mode and run for the TAGCLASS 'PM_TOT'. This error relates to aerosol indexing of water species.
2. The CMAQ-ISAM apportionment of the species 'AORGCJ' was not being calculated correctly, resulting in extremely high values (~E+20). 'AORGCJ' is tracked when the 'ALL' TAGCLASS is defined, but was not being properly tracked through aqueous chemistry. Additionally, 'MGLY' a precursor to 'AORGCJ' was missing from the CMAQ-ISAM gas species.
3. CMAQ-ISAM crashes when compiled in debug mode and run for the TAGCLASS 'ALL'. This error relates to CMAQ-ISAM tracking air density and incorrectly trying to do unit conversions on this species.
4. Ground level production and loss calculations in the deposition modules (M3DRY and STAGE) was incorrect.

Significance and Impact: No impact on CMAQ species concentrations found in the "CCTM_CONC* & CCTM_ACONC*" files.

1. The model no longer crashes in debug mode for the TAGCLASSES 'PM_TOT'.
2. The addition of 'MGLY' may impact O3 apportionment in some application. 'AORGCJ' apportionment no longer produces high values.
3. The model no longer crashes in debug mode for the TAGCLASSES 'ALL'.
4. The changes to ground level production and loss terms may impact a number of tracked CMAQ-ISAM species and TAGCLASSES depending on the case.

References: N/A
Internal PRs: PR#973

CMAQ-ISAM potential vorticity apportionment

Sergey L. Napelenok, U.S. Environmental Protection Agency
Type of update: Science Update
Release Version/Date: CMAQv5.5
Description: It is possible to apportion species in the OZONE TAGCLASS to ozone incursions at the top of the simulated volume if the base model is compiled with potential vorticity module enabled. For CMAQ-ISAM, this apportionment can be further subdivided by geographical region.
Significance and Impact: Ozone introduced at the top of the model can be tracked by specifying the keyword 'PVO3' in the 'EMIS STREAM(S)' section of the control file as follows:

TAG NAME        |PVO    
REGION(S)       |EVERYWHERE     
EMIS STREAM(S)  |PVO3   

Internal PRs: PR#957

CMAQ-ISAM version 5.4

Sergey L. Napelenok, U.S. Environmental Protection Agency
Type of update: Science Update
Release Version/Date: CMAQv5.4
Description:
The changes to ISAM include the added flexibility for the user to define how secondarily formed gaseous species are assigned to sources of parent reactants. Previously, daughter products were always assigned equally among the parents. However, in some applications, particularly in O3 apportionment, other assignment schemes are desired and requested by the users. The following options are now available in CMAQ-ISAM:

Option 1. Equal assignment (previous version).

Option 2. If parent reactants include the species NO, NO2, NO3, HONO, or ANO3, assignment to these sources only. Reactions without these species proceed with equal assignment.

Option 3. Option 2 with species list expanded to include reactive VOC species and radicals. Reactions without these species proceed with equal assignment.

Option 4. If parent reactants include the reactive VOC species and radicals, assignment to these sources only. Reactions without these species proceed with equal assignment.

Option 5. Assignment is based on the ratio of production H2O2 to production HNO3. Reactions without the nitrogen species listed above and reactive VOCs proceed with equal assignment.

Additionally, the transitional value for Option 5 is also customizable (default is PH2O2/PHNO3=0.35).

Significance and Impact: The changes here allow for greater ISAM user flexibility. Please, refer to the User's Guide chapter on ISAM for additional information.
References: Internal PRs PR#473, PR#571, PR#579, PR#620, PR#644, PR#649, PR#650, PR#655, PR#661, PR#657, PR#676, PR#699, PR#778, PR#698, PR#675

CMAQ-ISAM tagclasses for Hazardous Air Pollutants (HAPs)

William T. Hutzell, U.S. Environmental Protection Agency
Type of update: New Feature
Release Version/Date: CMAQv5.4
Description: Several tagclasses were added to CMAQ-ISAM to track the source contributions for HAPs. The below table lists the tagclasses and their HAPs.

Tagclass Name	HAPS1
HAP_GAS	formaldehyde, acetaldehyde, 1,3-butadiene, acrolein, molecular chlorine
HAP_AERO	aerosol bound nickle, lead, trivalent chromium, hexavalent chromium, beryllium, cadium, deisel emissions, manganese from the Air Toxics Inventory, and arsenic
PAH_TEQ	Polycycle Aromatic Compounds lumped based on Toxic Equivalancy Quotient
MERCURY	Gas and Aerosol Phases of Atmospheric Mercury
BENAPYRENE	Gas and Aerosol Phases of Benzo[a]pyrene

1. The exact species available per Tagclass depends on the chemical mechanism and the name-lists used.

Significance and Impact: Based on the chemical mechanism used, the new tagclasses allow simulating how the emissions source contribute to concentrations and deposition of HAPS in air toxic assessments.
Internal PRs: PR#922, PR#887, PR#773, PR#699