# Difference between SULF and SO2 in SMOKE

**URL:** <https://forum.cmascenter.org/t/difference-between-sulf-and-so2-in-smoke/1904>\
**Category:** Chemistry and Aerosols\
**Tags:** smoke\
**Created:** [November 10, 2020, 3:42pm UTC](https://forum.cmascenter.org/t/difference-between-sulf-and-so2-in-smoke/1904 "2020-11-10T15:42:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![skunwar](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@skunwar](https://forum.cmascenter.org/u/skunwar)\
**Post date:** [November 10, 2020, 3:42pm UTC](https://forum.cmascenter.org/t/difference-between-sulf-and-so2-in-smoke/1904/1 "2020-11-10T15:42:07Z")

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I am curious what the difference between species **SULF** and **SO2** is in SMOKE emissions files, since by default, in DESID, SULF from SMOKE maps to 0 as CMAQ gas species and maps fully to CMAQ fine aerosol species ASO4 while SO2 from SMOKE fully maps to CMAQ gas species SO2:

```
&EmissionScalingRules
 EM_NML=
 ! Region | Stream Label |Emission | CMAQ- |Phase/|Scale |Basis |Op  
 ! Label | |Surrogate| Species |Mode |Factor| |     
       ! Default Gases                                                                  
   'EVERYWHERE', 'ALL' ,'SO2' ,'SO2' ,'GAS' ,1. ,'UNIT','a', 
   'EVERYWHERE', 'ALL' ,'SULF' ,'SULF' ,'GAS' ,0. ,'UNIT','a', 

   ! Default Aerosols
   'EVERYWHERE', 'ALL' ,'SULF' ,'ASO4' ,'FINE' ,1. ,'MASS','a', 

```

When I do ‘ncdump’ of SMOKE emission files, I see the following description for SULF and SO2, and I couldn’t distinguish SULF from SO2:

```
    float SULF(TSTEP, LAY, ROW, COL) ;
            SULF:long_name = "SULF " ;
            SULF:units = "moles/s " ;
            SULF:var_desc = "Model species SULF " ;

    float SO2(TSTEP, LAY, ROW, COL) ;
            SO2:long_name = "SO2 " ;
            SO2:units = "moles/s " ;
            SO2:var_desc = "Model species SO2 " ;
```

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<div class="post-metadata">

**Author:** ![bbaek](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/bbaek/32/22_2.png) [@bbaek](https://forum.cmascenter.org/u/bbaek)\
**Post date:** [November 23, 2020, 3:28pm UTC](https://forum.cmascenter.org/t/difference-between-sulf-and-so2-in-smoke/1904/2 "2020-11-23T15:28:39Z")

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SULF represents “Sulfate as SO4”. SO2 and SULF are different. SULF (SO4) molecular weight is 96 grams.  
Not all cases, some sources use the following the SO2 speciation profiles to generate SO2 and SULF during the speciation processing in SMOKE. Some limited sources will generate an additional 2.86% of SO2 emissions as SULF.  
75014;“SO2”;“SULF”;0.0286;98.0;0.0286  
75014;“SO2”;“SO2”;1.0;64.0;1.0  
87514;“SO2”;“SULF”;0.0245;98.0;0.0245  
87514;“SO2”;“SO2”;1.0;64.0;1.0  
87514;“SOX”;“SULF”;0.0245;98.0;0.0245  
87514;“SOX”;“SO2”;1.0;64.0;1.0  
95014;“SO2”;“SULF”;0.0226;98.0;0.0226  
95014;“SO2”;“SO2”;1.0;64.0;1.0  
95014;“SOX”;“SULF”;0.0226;98.0;0.0226  
95014;“SOX”;“SO2”;1.0;64.0;1.0  
99010;“SO2”;“SULF”;0.0155;98.0;0.0155  
99010;“SO2”;“SO2”;1.0;64.0;1.0  
99010;“SOX”;“SULF”;0.0155;98.0;0.0155  
99010;“SOX”;“SO2”;1.0;64.0;1.0  
0000;“SO2”;“SO2”;1.0;64.0;1.0  
0000;“SO4”;“SULF”;1.0;96.0;1.0  
0000;“SOX”;“SO2”;1.0;64.0;1.0