How to output particulate water content and pH in CMAQ v5.5

[hosok004]

Hello, I am running a simulation with the cracmm2 mechanism in CMAQv5.5 and I was wondering if there was a way to output the water content and pH of PM2.5 species using the CCTM files. I found a section in the SpecDef_Conc_cracmm2.txt file that mentions some relevant variables, but I was unsure whether I would need to rerun my simulation to use these variables, as they are commented out by default (shown below).

Additionally, in an old forum post I found, it was mentioned that the species AORGH2O and AH2O represent particulate water content under ambient conditions. Although these species are listed in the AE_cracmm2.nml file, I did not see any listing of them in the cracmm2 SpecDef files. If I want to output this information will I need to make modifications to my species files to include these variables? I’ve included my cracmm2 files below for reference as well. Any clarification is appreciated. Thanks!

Relevant forum post: PM25 composition and estimation of PM25 water (CMAQv5.3.1)

SpecDef_cracmm2.txt (12.5 KB)

AE_cracmm2.nml.txt (8.7 KB)

SpecDef_Conc_cracmm2.txt (21.4 KB)

[Havala.Pye]

Hello,

Aerosol water (AORGH2O and AH2O) as well as H+ (AH3OPI/J) can be obtained from CONC or ACONC files. AORGH2O methods are documented in Pye et al. 2017 ACP; Fountoukis and Nenes 2007 ACP document AH2O and H+ produced by ISORROPIAII. You do not need to rerun CMAQ to get these in your A/CONC files. If you would like these species or the above quantities in your combine files, you will need to update the SpecDef and rerun combine. The lines are commented as the pH becomes undefined when aerosols are dry which will depend on RH and the domain being examined.

Havala

[hosok004]

Thanks for the help! I uncommented the AH2OIJ, HPMOLAL, ACIDITYTEMP, and FINEPHF lines in my SpecDef_Conc_cracmm2.txt file, added them to the SpecDef_cracmm2.txt file, and reran combine, and it looks like this resolved the issue.

I have a few more questions that I was hoping you could help clarify.

1. Does AH2OIJ only include water associated with inorganic fine PM? If so, to output the water content associated with organic fine PM could I simply add an additional line to the species files as follows?

AORGH2OIJ, ug m-3, AORGH2OI[1]+AORGH2OJ[1]

2. I noticed that there is a species variable called PM25_HP. Just to check that I understand correctly, does PM25_HP represent the total H+ concentration for all PM2.5 species (including organic aerosols), while HPMOLAL represents the H+ concentration of only the inorganic fine PM species (assuming AH2OIJ is nonzero)?

3. If I would like to only output aerosol water content and pH associated with inorganic PM2.5 (rather than from all fine PM), what would the best way to go about this? Could I simply add lines to my species files as follows?

!!H+ from inorganic PM2.5

PM25_AHPLUSIJ, umol m-3, (AH3OPI[1]*FPM25AIT[3]+AH3OPJ[1]*FPM25ACC[3])*1.0/19.0

!!H2O from inorganic PM2.5

PM25_AH2O, ug m-3, AH2OI[1]*FPM25AIT[3]+AH2OJ[1]*FPM25ACC[3]

!!Molar H+ concentration and pH from inorganic PM2.5

PM25_HPMOLAL, mol kg-1, (PM25_AHPLUSIJ[0]/PM25_AH2O[0])*1000.0

PM25_ACIDITYTEMP, , -1*LOG10(PM25_HPMOLAL[0])

PM25_FINEPHF, , PM25_AH2O[0]>0.01 ? PM25_ACIDITYTEMP[0] : -9.999E36

screenshots from SpecDef_Conc_cracmm2.txt:

[Havala.Pye]

Any particulate H+, whether a sharp size cut or modal sum, is only associated with the inorganic aerosols. We do not dissociated any organic species to H+.

1. AH2OI+AH2OJ is only water associated with inorganic species and comes from ISORROPIA.
2. PM25 implies a sharp size cut. See above–all H+ is inorganic associated.
3. Ignore AORGH2O if you do not want the water associated with organics.