pcVOC scale factor value of CMAQ v5.3

CMAQ Chemistry and Aerosols
1

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]

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

Best regards,
SH.LIM

2

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

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3

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

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