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12. Sulfur Tracking Method

12.1 Introduction

CMAQv5.3 includes 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 CTM 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_AE6I, SAPRC07TIC_AE7I, CB6R3_AE7, or CB6R3M_AE7 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

Shawn Roselle, Computational Exposure Division, U.S. EPA

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CMAQ User's Guide (c) 2019

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