CMAQv5.0.2 gas-phase chemistry

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New Mechanism: RACM2

Brief Description

Goliff et al. (2013) developed the Regional Atmospheric Chemistry Mechanism, Version 2 (RACM2). It consists of 363 chemical reactions and 33 photolytic reactions and is specifically designed for regional applications ranging from the Earth’s surface to the upper troposphere. RACM2 is implemented into the CMAQ model for the first time.

Significance and Impact

Sarwar et al. (2013) compared its predictions to those obtained with the CB05TU mechanism. RACM2 reduces monthly mean peroxyacetyl nitrate by 40%, organic nitrate by 41%, peroxyacetic acid by 94%, methyl hydroperoxide by 19%, while enhancing hydroxyl radical by 46%, ozone by 6%, sulfate by 10%, total nitrate by 22%, ammonium by 10%, and secondary organic aerosols by 10% compared to those obtained with the CB05TU.

Affected files

  • Mechanism dependent files (newly created):
    • mech.def, RXCM.EXT, RXDT.EXT
    • GC_racm2_ae6_aq.csv, AE_racm2_ae6_aq.csv, NR_racm2_ae6_aq.csv
    • GC_racm2_ae6_aq.nml, AE_racm2_ae6_aq.nml, NR_racm2_ae6_aq.nml
    • CSQY_DATA_racm2_ae6_aq
  • EBI solver (newly created):
    • hrcalcks.F, hrdata_mod.F, hrdriver.F, hrg1.F, hrg2.F, hrg3.F, hrg4.F, hrinit.F, hrprodloss.F, hrrates.F, hrsolver.F
  • Modified files:
    • SOA_DEFN.F (modified to include RACM2 dependent orgprod parent names)
    • hlconst.F (modified to include Henry's law constant for several RACM2 species)

References

  • Goliff, W. S., Stockwell, W. R., and Lawson, C. V. (2013), The Regional Atmospheric Chemistry Mechanism, Version 2, Atmospheric Environment, 68, 174–185.
  • Sarwar, G., et al. (2013), A comparison of atmospheric composition predicted with the Carbon Bond and the Regional Atmospheric Chemistry Mechanism, Atmospheric Chemistry and Physics, 13, 9695-9712.

Contact

Golam Sarwar, Atmospheric Modeling and Analysis Division, U.S. EPA

New Mechanism: SAPRC07TIC_AE6_AQ

Brief Description

A research version of the SAPRC07TC_AE6_AQ mechanism is included that has greater detail for chemistry of isoprene and the resultant daughter products. Xie et al. (2013) developed the mechanism and evaluated it using observations from Intercontinental Chemical Transport Experiment–North America/International Consortium for Atmospheric Research on Transport and Transformation during 2004.

Affected and New Files

  • New files under the MECHS/saprc07tic_ae6_aq directory:
    • mech_saprc07tic_ae6_aq.def, RXCM.EXT, RXDT.EXT
    • GC_saprc07tic_ae6_aq.nml, AE_saprc07tic_ae6_aq.nml, NR_saprc07tic_ae6_aq.nmlGC_racm2_ae6_aq.nml, CSQY_DATA_saprc07tic_ae6_aq
  • New files under the directory GAS/ebi_saprc07tic):
    • hrcalcks.F, hrdata_mod.F, hrdriver.F, hrg1.F, hrg2.F, hrg3.F, hrg4.F, hrinit.F, hrprodloss.F, hrrates.F, hrsolver.F
  • Modified files:
    • hlconst.F (modified to include Henry's law constant for new gas phase species)

Significance and Impact

The new mechanism has the potential to better account for how isoprene affects troposheric chemistry when VOC to NOx ratios are high. Consult the reference for details.

References

Y. Xie, F. Paulo, W. P. L. Carter, C. G. Nolte, D. J. Luecken, W. T. Hutzell, P. O.Wennberg, R. C. Cohen, and R.W. Pinder, 2013. Understanding the impact of recent advances in isoprene photooxidation on simulations of regional air quality. Atmos. Chem. Phys., 13, 8439–8455

Contact

Deborah L. Luecken, Atmospheric Modeling and Analysis Division, U.S. EPA

Error: CB05TUMP_AE6_AQ

Brief Description

Version 5.0 and 5.01 of the mechanism unintentionally duplicated ten reactions that involved benzene, sesquitenes and secondary aerosol precusors from xylenes and toulene. The duplicates were removed from the mechanism by modifying the below files.

Affected files

  • Modified files under the MECHS/cb05tump_ae6_aq directory:
    • mech_cb05tump_ae6_aq.def, RXCM.EXT, RXDT.EXT,
  • Modified files under new under the directory GAS/ebi_cb05tump:
    • hrcalcks.F, hrdata_mod.F, hrdriver.F, hrg1.F, hrg2.F, hrg3.F, hrg4.F, hrinit.F, hrprodloss.F, hrrates.F, hrsolver.F

Significance and Impact

The change removes an error in the predicted concentrations of benzene, sesquitenes and secondary aerosol precusors from xylenes and toulene.

References

None

Contact

William T. Hutzell, Atmospheric Modeling and Analysis Division, U.S. EPA

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