CMAQv5.0 PMother speciation

Heather Simon

Changes required to speciate PM_other can be classified into two types: 1) changes made to the emissions and 2) changes made to the CMAQ model. These two changes are summarized here:

Emissions

Previously, primary PM_2.5 emissions were split into 5 species: OC, EC, sulfate, nitrate, and PMFINE (unspeciated). We now split primary PM_2.5 emissions into 18 species: OC, EC, sulfate, nitrate, H₂O, Na⁺, Cl^-, NH₄⁺, non-carbon organic matter (NCOM), Al, Ca²⁺, Fe, Si, Ti, Mg²⁺, K⁺, Mn, and Other (note that PMFINE is now called PMOTHR). The speciation profiles are taken directly from Reff et al. (2009).

• Four species were explicitly treated in previous versions of CMAQ but were not modeled as being emitted from anthropogenic sources: H₂O, Na⁺, Cl^-, and NH₄⁺.
• NCOM is needed to accurately model total organic mass.
• Al, Ca²⁺, Fe, Si, and Ti are major crustal elements and are useful for evaluations against IMPROVE’s dust measurements.
• Mg²⁺, K⁺, and Ca²⁺ are inputs for ISORROPIAv2.1.
• Fe and Mn are catalysts for aqueous-phase SO₂ oxidation. Model estimates of Fe and Mn concentrations now replace default values that were used in previous versions of CMAQ as described in the ISORROPIAv2.1 section of the release notes.

CMAQ code changes

Name changes: We have changed the names of two model species in CMAQ. AORGPAI and AORGPAJ are now called APOCI and APOCJ to clarify that these species represent primary carbon and not primary organic mass. A25I and A25J have been renamed AOTHRI and AOTHRJ to clarify that this species represents the remaining unspeciated mass and not total PM_2.5 mass.

Emissions of four previously existing species: CMAQ was modified to allow H₂O, Na⁺, Cl^-, and NH₄⁺ to be emitted from anthropogenic sources. PM concentrations estimates are expected to change due to the fact that some mass which was previously considered unspeciated primary PM (A25J in the model) is now assigned to these four species. Previously, NH₄⁺ was purely a secondary PM species, Na⁺ was only emitted from sea spray, and Cl^- was both a secondary species and emitted from sea spray. These three species all participate in equilibrium reactions (represented by ISORROPIA). Therefore, although the emitted mass now assigned to these species was previously nonvolatile and inert (as part of A25J), now NH₄⁺ and Cl^- can partition and sodium can affect how other species partition. Particulate water mass is controlled completely by thermodynamic partitioning in ISORROPIA. This partitioning is driven by RH (the amount of water in the particle phase is small compared to that in the air, so particulate water concentrations do not affect this partitioning). Therefore, the emission of H₂O should not affect how much particulate water is present in the model. The effect of assigning some PMFINE mass to H₂O is that this portion of the PM mass volatilizes, therefore decreasing the total primary PM concentrations in CMAQ.

New modeled species: Nine new PM species were added to CMAQ: APNCOMI/J,AALJ, ACAJ, AFEJ, ASIJ, ATIJ, AMGJ, AKJ, and AMNJ. Three of these species (Mg²⁺, K⁺, and Ca²⁺) are being incorporated into ISORROPIAv2.1 so they participate in thermodynamic partitioning of inorganic particles. Two other species (Fe and Mn) have been brought into the cloud module and now participate in the oxidation of SO₂ to sulfate. Although these two species can act as aqueous catalysts, they themselves are inert and non-volatile. The other metals (Al, Si, and Ti) are treated as inert and non-volatile like the old A25J species. Non-carbon organic mass (APNCOM) is non-volatile and the chemistry associated with this PM component is described in the POA aging section of the release notes. Physical parameters for all emitted species are shown in Table 1.

Effect of Changes: Some changes are expected to affect total PM_2.5 concentrations. These changes are listed below:

1. Emissions of PMFINE used to all be assigned to A25J (non-volatile). Now PMFINE has been speciated into some compounds that can partition between the gas and particle phases (NH₄⁺, H₂O, Cl^-)
2. Old PMFINE emissions did not affect ISORROPIA. Now the NH₄⁺, Na⁺, and Cl^-, Mg²⁺, K⁺, and Ca²⁺ are being emitted from anthropogenic sources, this may affect partitioning of other species in ISORROPIA (nitrate). Changes associated with updates to ISORROPIAv2.1 are explained in more detail separately.
3. MW for PMFINE speciated compounds are different than MW for A25J
4. 100% of PMFINE used to be assigned to the J mode. Now, one speciated compound (NCOM) is split between I and J modes
5. Density used in calculations of 3rd moment has changed for some components. A25J used ANTHFAC. Now NCOM uses ORGFAC and NH₄⁺ uses NH4FAC.
6. Changes associated with updates to the cloud module are described separately

Table 1: Physical parameters for emitted PM species in CMAQ. No changes have been made to species highlighted in blue. The name changed for species highlighted in yellow. Species highlighted in green were existing CMAQ species that were not previously emitted from anthropogenic sources. Species highlighted in purple are new CMAQ species.

Species	Emitted Species Name***	Modeled Species Name	Emitted Species Name in CMAQv4.7.1	Modeled Species Name in CMAQv4.7.1	Molecular Weight (g/mol)	Density (g/cm3)	Charge	Volatility	Fraction Emitted in J Mode	Fraction Emitted in I Mode
Elemental Carbon	PEC	AECI/J	PEC	AECI/J	12	2.2	0	Nonvolatile	0.999	0.001
Sulfate	PSO4	ASO4I/J	PSO4	ASO4I/J	96	1.8	-2	Nonvolatile but participates in ISORROPIA	1.000	0
Nitrate	PNO3	ANO3I/J	PNO3	ANO3I/J	62	1.8	-1	Semivolatile	1.000	0
Primary un-speciated coarse PM	PMC	ACORS	PMC	ACORS	100	2.2	0	Nonvolatile but participates in ISORROPIA*	0	0
Primary organic carbon	POC	APOCI/J	POC	AORGPAI/J	220	2.0	0	Nonvolatile	0.999	0.001
Primary un-speciated fine PM	PMOTHR	AOTHRJ	PMFINE	A25J	200	2.2	0	Nonvolatile	1.000	0
Water	PH2O	AH2OJ	PMFINE	A25J(primary); AH2OJ(secondary)	18	1.0	0	Semivolatile	1.000	0
Sodium	PNA	ANAJ	PMFINE	A25J(anthropogenic); ANAJ(seasalt)	23	2.2	+1	Nonvolatile but participates in ISORROPIA	1.000	0
Chloride	PCL	ACLJ	PMFINE	A25J(primary); ACLJ(seasalt/secondary)	35	2.2	-1	Semivolatile	1.000	0
Ammonium	PNH4	ANH4J	PMFINE	A25J(primary); ANH4J(secondary)	18	1.8	+1	Semivolatile	1.000	0
Primary non-carbon organic mass	PNCOM	APNCOMI/J	PMFINE	A25J	220	2.0	0	Nonvolatile	0.999	0.001
Aluminum	PAL	AALJ	PMFINE	A25J	27	2.2	0	Nonvolatile	1.000	0
Calcium	PCA	ACAJ	PMFINE	A25J	40	2.2	+2	Nonvolatile but participates in ISORROPIA	1.000	0
Iron	PFE	AFEJ	PMFINE	A25J	56	2.2	0**	Nonvolatile	1.000	0
Silicon	PSI	ASIJ	PMFINE	A25J	28	2.2	0	Nonvolatile	1.000	0
Titanium	PTI	ATIJ	PMFINE	A25J	48	2.2	0	Nonvolatile	1.000	0
Magnesium	PMG	AMGJ	PMFINE	A25J	24.3	2.2	+2	Nonvolatile but participates in ISORROPIA	1.000	0
Potassium	PK	AKJ	PMFINE	A25J	39	2.2	+1	Nonvolatile but participates in ISORROPIA	1.000	0
Manganese	PMN	AMNJ	PMFINE	A25J	55	2.2	0**	Nonvolatile	1.000	0

\*note: In the implementation of ISORROPIAv2.1 into CMAQ, a static speciation profile is applied to ACORS and the portions of ACORS attributed to thermodynamically active species (Na⁺, Ca²⁺, K⁺, Mg²⁺) are used as inputs to the ISORROPIA module

\**note: Iron and Manganese are represented as having a charge of 0 in AERO_DATA. However, we assume oxidation states for these compounds in the aqueous chemistry module: Fe is assumed to be 90% Fe(III) at night and 10% Fe(III) during the daytime; Mn is assumed to be 100% Mn(II).

\***note: The emitted species name cannot be changed in the AE namelist file. It is set in AERO_DATA.F with emissions read in GET_AERO_EMIS of AERO_EMIS.F

Affected files: AERO_DATA.F, AE_cb05cl_ae5_aq_recon.nml, AE_cb05cl_ae5_aq_recon.csv

References:

Reff, A., Bhave, P.V., Simon, H., Pace, T.G., Pouliot, G.A., Mobley, J.D., Houyoux, M. (2009) Emissions Inventory of PM2.5 Trace Elements across the United States, Environmental Science and Technology, 43, 5790-5796