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12. Sulfur Tracking Method#

12.1 Introduction#

Starting with CMAQv5.3, a runtime diagnostic model option that provides detailed information on the modeled sulfur budget. This option, referred to as the “Sulfur Tracking Method (STM)”, tracks sulfate production from gas- and aqueous-phase chemical reactions, as well as contributions from emissions and initial and boundary conditions. Each tracked species is treated as other modeled species, undergoing transport (advection, diffusion, cloud-mixing) and removal by deposition (both wet and dry). Several notable features in the CMAQv5.3 release of STM include:

The STM is now a runtime option enabled by an environment variable.
Additional species (Table 12-2) are included to track the loss of inorganic sulfate to organosulfate for chemical mechanisms that include this loss pathway.

12.2 Usage#

To activate the STM option, edit the CCTM runscript and set the following environment variable to “Y” (the default is “N”):

setenv STM_SO4TRACK Y

The STM option does not require any additional input files, and uses the initial conditions, boundary conditions, and emissions files available for with the standard, non-instrumented CCTM.

Next, run the CMAQ CTM following the instructions described in Chapter 5, section 5.7.

Note that several of the standard CMAQ output files (ACONC, CONC, CGRID, DDEP, and WDEP) will include additional species beyond the standard base model species list. A list of the additional species output by the STM option are provided in Table 12-1 and Table 12-2. These data can be post-processed using standard utilities, such as:

combine (to combine multiple days into one file or to aggregate various tracking species)
m3tproc (to sum/average over multiple days)
verdi (for data visualization)

Table 12-1. Sulfur Tracking Species List

Species Group	Species Name	MW	Description
AE	ASO4AQH2O2J	96.0	Accumulation mode sulfate (ASO4J) produced by aqueous-phase hydrogen peroxide oxidation reaction: H₂O₂ + S(IV) -> S(VI) + H₂O
AE	ASO4AQO3J	96.0	ASO4J produced by aqueous-phase ozone oxidation reaction: O₃ + S(IV) -> S(VI) + O₂
AE	ASO4AQFEMNJ	96.0	ASO4J produced by aqueous-phase oxygen catalyzed by Fe³⁺ and Mn²⁺ oxidation reaction: O₂ + S(IV) -> S(VI)
AE	ASO4AQMHPJ	96.0	ASO4J produced by aqueous-phase methyl hydrogen peroxide oxidation reaction: MHP + S(IV) -> S(VI)
AE	ASO4AQPAAJ	96.0	ASO4J produced by aqueous-phase peroxyacetic acid oxidation reaction: PAA + S(IV) -> S(VI)
AE	ASO4GASJ	96.0	ASO4J condensation following gas-phase reaction: OH + SO₂ -> SULF + HO₂
AE	ASO4EMISJ	96.0	ASO4J from source emissions
AE	ASO4ICBCJ	96.0	ASO4J from boundary and initial conditions
AE	ASO4GASI	96.0	Aitken mode sulfate (ASO4I) nucleation and/or condensation following gas-phase reaction: OH + SO₂ -> SULF + HO₂
AE	ASO4EMISI	96.0	ASO4I from source emissions
AE	ASO4ICBCI	96.0	ASO4I from boundary and initial conditions
AE	ASO4GASK	96.0	Coarse mode sulfate (ASO4K) condensation following gas-phase reaction: OH + SO₂ -> SULF + HO₂
AE	ASO4EMISK	96.0	ASO4K from source emissions
AE	ASO4ICBCK	96.0	ASO4K from boundary and initial conditions
NR	SULF_ICBC	98.0	Sulfuric acid vapor (SULF) from boundary and initial conditions

Table 12-2. Additional Tracking Species Representing Loss of Inorganic Sulfate to Organosulfate (only included if using SAPRC07TIC_AE7I, CB6R3_AE7, CB6R5_AE7,CB6R5M_AE7, CRACMM1 or CRACMM1AMORE based mechanisms)

Species Group	Species Name	MW	Description
AE	OSO4J	96.0	Loss of ASO4J to organosulfate
AE	OSO4AQH2O2J	96.0	Loss of ASO4AQH2O2J to organosulfate
AE	OSO4AQO3J	96.0	Loss of ASO4AQO3J to organosulfate
AE	OSO4AQFEMNJ	96.0	Loss of ASO4AQFEMNJ to organosulfate
AE	OSO4AQMHPJ	96.0	Loss of ASO4AQMHPJ to organosulfate
AE	OSO4AQPAAJ	96.0	Loss of ASO4AQPAAJ to organosulfate
AE	OSO4GASJ	96.0	Loss of ASO4GASJ to organosulfate
AE	OSO4EMISJ	96.0	Loss of ASO4EMISJ to organosulfate
AE	OSO4ICBCJ	96.0	Loss of ASO4ICBCJ to organosulfate

Contact

William T. Hutzell , U.S. EPA

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CMAQv5.5 User’s Guide