CMAQv5.1 Integration of gas and heterogeneous chemistry

Brief Description

Heterogeneous chemistry is now listed in the mech.def file and solved simulataneously with the gas phase chemistry in CMAQv5.1. This allows a more accurate calculation of reaction rates that are dependant on rapidly-changing radical concentrations and allows easier access to the entire set of reactions that are occurring. In CMAQ v5.0.2 and earlier versions, the heterogeneous reactions were treated in an ad-hoc manner depending on the reaction.

Significance and Impact

This change makes it easier to modify and organize the gas, aerosol and surface chemical reactions and allows for more accurate solution of heterogeneous reactions that include fast-reacting radical species. It has little impact on CMAQ predictions or run time.

Affected files

Modified modules:

• MECHS: all mechanisms (cb05e51_ae6_aq, racm2_ae6_aq, saprc07tb_ae6_aq, saprc07tc_ae6_aq, etc.)
• aero: aero6, aero6_mp, aero6i

Additional Information

The following reactions have been added to the photochemical mechanism definition files, commonly referred to as the mech.def files.

Heterogeneous hydrolysis of alkyl nitrates (CB05e51 only; new to CMAQv5.1; for more info see Changes to CB05: NOy updates/additions, isoprene extensions and misc.):

<HET_NT1> NTRALK = HNO3                # 1.0~<HETERO_NTR2>;
<HET_NT2> NTROH = HNO3                 # 1.0~<HETERO_NTR2>;
<HET_NT3> NTRCN = HNO3                 # 1.0~<HETERO_NTR2>;
<HET_NT4> NTRCNOH = HNO3               # 1.0~<HETERO_NTR2>;
<HET_NT5> NTRPX = HNO3                 # 1.0~<HETERO_NTR2>;
<HET_NT6> NTRM = HNO3                  # 1.0~<HETERO_NTR2>;
<HET_NT7> NTRI = HNO3                  # 1.0~<HETERO_NTR2>;

Heterogeneous hydrolysis of N2O5 and production of nitryl chloride (all mechanisms; new to CMAQv5.1; for more info see CMAQv5.1 ClNO2 chemistry):

<HET_N2O5IJ>    N2O5 = HNO3 + H2NO3PIJ  # 1.0~<HETERO_N2O5IJ>;
<HET_N2O5K>     N2O5 = HNO3 + H2NO3PK   # 1.0~<HETERO_N2O5K>;
<HET_H2NO3PIJA> H2NO3PIJ = HNO3         # 1.0~<HETERO_H2NO3PAIJ>;
<HET_H2NO3PKA>  H2NO3PK  = HNO3         # 1.0~<HETERO_H2NO3PAK>;
<HET_H2NO3PIB>  H2NO3PIJ + ACLI = CLNO2 # 1.0~<HETERO_H2NO3PBIJ>;
<HET_H2NO3PJB>  H2NO3PIJ + ACLJ = CLNO2 # 1.0~<HETERO_H2NO3PBIJ>;
<HET_H2NO3PKB>  H2NO3PK  + ACLK = CLNO2 # 1.0~<HETERO_H2NO3PBK>;

Surface production of HONO from NO2 (all mechanisms; previously available in CMAQv5.0.2):

<HET_N02> NO2 = 0.5*HONO + 0.5*HNO3 # 1.0~<HETERO_NO2>;

Heterogeneous production of SOA from IEPOX (all mechanisms; new to CMAQ v5.1; for more info see SOA updates)

<HET_IEPOX> IEPOX = AISO3J  # 1.0~<HETERO_IEPOX>;

Oligomerization reaction for secondary organic aerosols (all mechanisms; previously in CMAQ v5.0.2):

<OLIG_XYLENE1>    AXYL1J = 1.1428*AOLGAJ  # 9.48816E-6;
<OLIG_XYLENE2>    AXYL2J = 1.1428*AOLGAJ  # 9.48816E-6;
<OLIG_TOLUENE1>   ATOL1J = 1.0000*AOLGAJ  # 9.48816E-6;
<OLIG_TOLUENE2>   ATOL2J = 1.0000*AOLGAJ  # 9.48816E-6;
<OLIG_BENZENE1>   ABNZ1J = 0.85714*AOLGAJ # 9.48816E-6;
<OLIG_BENZENE2>   ABNZ2J = 0.85714*AOLGAJ # 9.48816E-6;
<OLIG_TERPENE1>   ATRP1J = 1.0000*AOLGBJ  # 9.48816E-6;
<OLIG_TERPENE2>   ATRP2J = 1.0000*AOLGBJ  # 9.48816E-6;
<OLIG_ISOPRENE1>  AISO1J = 0.50*AOLGBJ    # 9.48816E-6;
<OLIG_ISOPRENE2>  AISO2J = 0.50*AOLGBJ    # 9.48816E-6;
<OLIG_SESQT1>     ASQTJ  = 1.50*AOLGBJ    # 9.48816E-6;
<OLIG_PAH1>       APAH1J = 1.4286*AOLGAJ  # 9.48816E-6;
<OLIG_PAH2>       APAH2J = 1.4286*AOLGAJ  # 9.48816E-6;
<OLIG_ALK1>       AALK1J = 1.7143*AOLGAJ  # 9.48816E-6;
<OLIG_ALK2>       AALK2J = 1.7143*AOLGAJ  # 9.48816E-6;

Aging reactions for primary organic carbon (all mechanisms; previously in CMAQ v5.0.2):

<RPOAGEPI> APOCI   + OH = 1.25*APNCOMI + APOCI + OH # 2.5E-12;
<RPOAGELI> APNCOMI + OH = OH                        # 1.0~<HETERO_PNCOMLI>;
<RPOAGEPJ> APOCJ   + OH = 1.25*APNCOMJ + APOCJ + OH # 2.5E-12;
<RPOAGELJ> APNCOMJ + OH = OH                        # 1.0~<HETERO_PNCOMLJ>;

Contact

William T. Hutzell, National Exposure Research Laboratory, U.S. EPA