What's CHEM in Process Analysis for PM2.5?

Hi,
In the integrated process rate(IPR) analysis of Process Analysis module in CMAQv5.3.1, CHEM means “Chemistry”.
I used IPR to do the analysis for PM2.5, and it was defined in pa_cb6r3_ae7_aq.ctl as follows:

DEFINE FAMILY ATOTI = ASO4I+ANO3I+ANH4I+ANAI+ACLI+AECI+AOTHRI+ALVPO1I + ASVPO1I + ASVPO2I + APOCI  +APNCOMI+ ALVOO1I + ALVOO2I + ASVOO1I + ASVOO2I;
DEFINE FAMILY ATOTJ = ASO4J+ANO3J+ANH4J+ANAJ+ACLJ+AECJ+AOTHRJ+AFEJ+ASIJ+ATIJ+ACAJ+AMGJ+AMNJ+AK+AALJ+ALVPO1J+ASVPO1J+ASVPO2J+APOCJ+ASVPO3J+AIVPO1J+APNCOMJ+AISO1J+ AISO2J  + AISO3J   +AMT1J   + AMT2J   + AMT3J+ AMT4J  +AMT5J   + AMT6J   + AMTNO3J+AMTHYDJ + AGLYJ   + ASQTJ+AORGCJ+ AOLGBJ  + AOLGAJ +ALVOO1J + ALVOO2J + ASVOO1J + ASVOO2J+ASVOO3J + APCSOJ+ AAVB1J + AAVB2J+AAVB3J + AAVB4J;
DEFINE FAMILY ATOTK = ASOIL+ACORS+ASEACAT+ACLK+ASO4K+ANO3K+ANH4K;

IPR_OUTPUT ATOTI;
IPR_OUTPUT ATOTJ;
IPR_OUTPUT ATOTK;

The following results are included:

  IPR_OUTPUT( 22) = ZADV of ATOTI           
  IPR_OUTPUT( 23) = HADV of ATOTI           
  IPR_OUTPUT( 24) = HDIF of ATOTI           
  IPR_OUTPUT( 25) = VDIF of ATOTI           
  IPR_OUTPUT( 26) = EMIS of ATOTI           
  IPR_OUTPUT( 27) = DDEP of ATOTI           
  IPR_OUTPUT( 28) = CLDS of ATOTI           
  IPR_OUTPUT( 29) = CHEM of ATOTI           
  IPR_OUTPUT( 30) = COND of ATOTI           
  IPR_OUTPUT( 31) = COAG of ATOTI           
  IPR_OUTPUT( 32) = GROW of ATOTI           
  IPR_OUTPUT( 33) = NPF of ATOTI           

There exists CHEM for PM2.5 and not equal to zero.

The CHEM in the CMAQ model mainly represents the gas-phase chemical process. Here, what are the gas-phase chemical reactions that contribute to the PM2.5 formation? Or it includes the gas-particle heterogeneous reactions? And what are they?

Thanks!
C.W.Huang

Hi C.W.,

You are right. These are the heterogeneous reactions. You can look for aerosol species involved in reactions in the mechanism definition file here: CMAQ/mech_cb6r3_ae7_aq.def at master · USEPA/CMAQ · GitHub

Generally, particulate chloride (ACLI and ACLJ) are lost while ANO3 species are produced (see reactions beginning with “HET_” label). There are also heterogeneous reactions contributing to formation of isoprene SOA (AISO3J) via IEPOX uptake, hydrolysis of Monoterpene SOA (AMTNO3J to AMTHYDJ) and oligomerization of AAVB, AISO1, AISO2, and ASQT species to form AOLGAJ and AOLGBJ.

You can see the production and loss of each of these reaction directly in CMAQ/hrprodloss.F at master · USEPA/CMAQ · GitHub

Best wishes,
Ben Murphy

2 Likes

Thanks for the detailed response. It helped me a lot.

Best wishes,
C.W.Huang