# pcVOC scale factor value of CMAQ v5.3

**URL:** <https://forum.cmascenter.org/t/pcvoc-scale-factor-value-of-cmaq-v5-3/5083>\
**Category:** Chemistry and Aerosols\
**Tags:** cmaq\
**Created:** [July 17, 2024, 5:45pm UTC](https://forum.cmascenter.org/t/pcvoc-scale-factor-value-of-cmaq-v5-3/5083 "2024-07-17T17:45:09Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![SH.LIM](https://avatars.discourse-cdn.com/v4/letter/s/5f8ce5/32.png) [@SH.LIM](https://forum.cmascenter.org/u/SH.LIM)\
**Post date:** [July 17, 2024, 5:45pm UTC](https://forum.cmascenter.org/t/pcvoc-scale-factor-value-of-cmaq-v5-3/5083/1 "2024-07-17T17:45:09Z")

</div>

Hi,

I have a question about the pcVOC scale factor value of CMAQ v5.3.  
I am collecting data to simulate SOA to factor values that are more suitable for KOREA.  
I am trying to use the **cb6r3\_ae7\_aq mechanism of CMAQ v5.3.2**.

! pcSOA is a CMAQ species introduced to account for missing pathways for SOA  
! formation from combustion sources. It includes IVOC oxidation as well as other  
! phenomena (Murphy et al., ACP, 2017). It was parameterized primarily in LA,  
! where vehicle exhaust continues to dominate.  
‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘PCVOC’ ,‘GAS’ ,6.579,‘MASS’,‘a’,  
‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘PCVOC’ ,‘GAS’ ,6.579,‘MASS’,‘a’,  
! However, the added pcSOA is probably inappropriate for Fire sources, especially  
! in its current configuration. This pathway should be zeroed out for all fire  
! and wood-burning related sources.  
‘EVERYWHERE’, ‘PT\_FIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,  
‘EVERYWHERE’, ‘PT\_RXFIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,  
‘EVERYWHERE’, ‘PT\_AGFIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,  
‘EVERYWHERE’, ‘PT\_OTHFIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,  
‘EVERYWHERE’, ‘PT\_FIRES\_MXCA’,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,  
‘EVERYWHERE’, ‘GR\_RES\_FIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,

Above is **cb6r3\_ae7\_aq.nml of CMAQ v5.3.2**.  
It is stated that the pcVOC scale factor values use **6.579** values according to **(Murphy et al., ACP, 2017)**.

But I couldn’t find the 6.579 value.  
This value is optimized for which region (e.g. U.S.), and I would like to know the exact source or calculation method.  
Also, I would like to know if the unit of 6.579 value is **mole-pcVOC/g-POA**.

In addition, Mr. Murphy recommended **0.0387** as _the default for the pcVOC scale factor in the GC\_cb6r3\_ae6\_aq mechanism of CMAQv5.2_. [[How to activate VBS in CMAQ v5.2? - #3 by shigan\_liu](https://forum.cmascenter.org/t/how-to-activate-vbs-in-cmaq-v5-2/3158/3)]

I’m also curious why the value difference between 6.579 and 0.0387 is large.

Best regards,  
SH.LIM

---

<div class="post-metadata">

**Author:** ![Ben\_Murphy](https://avatars.discourse-cdn.com/v4/letter/b/74df32/32.png) [@Ben\_Murphy](https://forum.cmascenter.org/u/Ben_Murphy)\
**Post date:** [July 17, 2024, 9:13pm UTC](https://forum.cmascenter.org/t/pcvoc-scale-factor-value-of-cmaq-v5-3/5083/2 "2024-07-17T21:13:14Z")

</div>

Hello,

Thanks for your questions. The value 0.0387 is in units of [mol pcVOC / g POA] as indicated in Table 4 of Murphy et al. (2017). The value 6.579 is obtained when 0.0387 is multiplied by the molecular weight of pcVOC, 170 g/mol, to get units of [g pcVOC / g POA].

The DESID module automatically converts mass to mole units when conserving mass and populating a gas variable in CMAQ.

Cheers,  
Ben

---

<div class="post-metadata">

**Author:** ![SH.LIM](https://avatars.discourse-cdn.com/v4/letter/s/5f8ce5/32.png) [@SH.LIM](https://forum.cmascenter.org/u/SH.LIM)\
**Post date:** [July 18, 2024, 8:43am UTC](https://forum.cmascenter.org/t/pcvoc-scale-factor-value-of-cmaq-v5-3/5083/3 "2024-07-18T08:43:28Z")

</div>

Thank you for answering my question!  
Your response was incredibly helpful and informative.  
I really appreciate you taking the time to share your knowledge with me.

Thanks again,  
SH.LIM