CMAQv5.0 PMother speciation
Changes required to speciate PMother 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:
Previously, primary PM2.5 emissions were split into 5 species: OC, EC, sulfate, nitrate, and PMFINE (unspeciated). We now split primary PM2.5 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 PM2.5 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 PM2.5 concentrations. These changes are listed below:
- 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-)
- 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.
- MW for PMFINE speciated compounds are different than MW for A25J
- 100% of PMFINE used to be assigned to the J mode. Now, one speciated compound (NCOM) is split between I and J modes
- Density used in calculations of 3rd moment has changed for some components. A25J used ANTHFAC. Now NCOM uses ORGFAC and NH4+ uses NH4FAC.
- 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|
|Sulfate||PSO4||ASO4I/J||PSO4||ASO4I/J||96||1.8||-2||Nonvolatile but participates in ISORROPIA||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|
|Sodium||PNA||ANAJ||PMFINE||A25J(anthropogenic); ANAJ(seasalt)||23||2.2||+1||Nonvolatile but participates in ISORROPIA||1.000||0|
|Primary non-carbon organic mass||PNCOM||APNCOMI/J||PMFINE||A25J||220||2.0||0||Nonvolatile||0.999||0.001|
|Calcium||PCA||ACAJ||PMFINE||A25J||40||2.2||+2||Nonvolatile but participates in ISORROPIA||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|
\*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
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