CMAQv5.4 Release Notes: Chemistry: Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) - fisidi/CMAQ GitHub Wiki

The Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) Version 1.0

Havala O. T. Pye, U.S. Environmental Protection Agency
Type of update: Science Update
Release Version/Date: CMAQv5.4
Description: The Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) builds on the history of the Regional Atmospheric Chemistry Mechanism, Version 2 (RACM2) and aims to couple gas- and particle-phase chemistry by treating the entire pool of atmospheric reactive organic carbon (ROC) relevant to present-day emissions. CRACMM species were developed to represent the total emissions of ROC, considering the OH reactivity, ability to form ozone and secondary organic aerosol (SOA), and other properties of individual emitted compounds. The chemistry of CRACMM, which includes autoxidation, multigenerational oxidation, and the treatment of semivolatile and intermediate volatility compounds, was built using a variety of sources including literature and other mechanisms (MCM, GECKO, and SAPRC18/mechgen). Compared to RACM2, the number of traditional volatile organic carbon species is reduced and the number of oxygenated and semivolatile to intermediate volatility precursors are increased in the mechanism. In addition, explicit hazardous air pollutants (toluene; 1,3-butadiene; and acrolein) are added to better characterize exposures relevant for human health.

CRACMMv1 is available in two versions: base CRACMMv1 and CRACMMv1AMORE. The development of base CRACMMv1 is described by Pye et al. and the application of CRACMMv1 within CMAQ to the northeast U.S. in summer 2018 as well as comparison with other mechanisms is presented by Place et al. CRACMMv1AMORE replaces the base isoprene chemistry of CRACMMv1 (which was largely ported from RACM2) with a graph theory-based condensation of a detailed isoprene mechanism developed by Prof. Faye McNeill's team at Columbia University. The AMORE version is documented in work by Wiser et al.

One feature of CRACMM is the specification of representative structures for all species in the mechanism. Metadata, including a representative compound name, description of explicit vs lumped nature, a SMILES string, and DTXSID identifier in the EPA Chemicals Dashboard (if available) are appended to the species namelists (GC, NR, and AE). This information is leveraged to determine conservation of mass across chemical reactions (see the CHEMMECH README in the UTIL directory), determination of species properties such as solubility, and to communicate how species are conceptualized. Representative compound information from the namelists are matched with species descriptions (a verbose string description in cracmm1_speciesdescription.csv) using python to provide markdown file descriptions of the mechanism species. See the CMAQ Users' Guide Chapter 6 for more information on CRACMM.

Supporting data for CRACMM, including information on how to map emissions to the mechanism, will be available in a CRACMM github repository.

Significance and Impact: CRACMM couples SOA formation with radical chemistry and updates the representation of a number of chemical systems. CRACMM is being released as a research mechanism so that it may undergo testing in various applications with the aim of making it the default chemistry option in the future. A fact sheet describing the CRACMM effort is available on EPA's CMAQ website.

References:

  1. Pye, H., B. Place, B. Murphy, K. Seltzer, C. Allen, I. Piletic, E. D'Ambro, R. Schwantes, M. Coggon, S. Farrell, E. Saunders, L. Xu, G. Sarwar, W. Hutzell, K. Foley, G. Pouliot and W. Stockwell, Linking Gas, Particulate, and Toxic Endpoints to Air Emissions In The Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 1.0, in preparation for Atmospheric Chemistry and Physics.
  2. Place, B, K. Seltzer, C. Allen, B. Murphy, K. Appel, I. Piletic, E. D'Ambro, R. Schwantes, M. Coggon, S. Farrell, E. Saunders, L. Xu, G. Sarwar, W. Hutzell, W. Stockwell, A. Torres-Vazquez, J. Pleim and H. Pye, Application of the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) to simulation of air quality in the Northeast USA, in preparation for Atmospheric Chemistry and Physics.
  3. Wiser, F., B. Place, H. Pye, and V. F. McNeill, Development and application of the AMORE isoprene chemistry condensation, in preparation for Geoscientific Model Development.

Internal PRs: PR#908