Chemical transport model

A chemical transport model (CTM) is a type of computer numerical model which typically simulates atmospheric chemistry and may give air pollution forecasting.

Chemical transport models and general circulation models

While related general circulation models (GCMs) focus on simulating overall atmospheric dynamics (e.g. fluid and heat flows), a CTM instead focuses on the stocks and flows of one or more chemical species. Similarly, a CTM must solve only the continuity equation for its species of interest, a GCM must solve all the primitive equations for the atmosphere; but a CTM will be expected to accurately represent the entire cycle for the species of interest, including fluxes (e.g. advection), chemical production/loss, and deposition. That being said, the tendency, especially as the cost of computing declines over time, is for GCMs to incorporate CTMs for species of special interest to climate dynamics, especially shorter-lived species such as nitrogen oxides and volatile organic compounds; this allows feedbacks from the CTM to the GCM's radiation calculations, and also allows the meteorological fields forcing the CTM to be updated at higher time resolution than may be practical in studies with offline CTMs.

Types of chemical transport models

CTMs may be classified according to their methodology and their species of interest, as well as more generic characteristics (e.g. dimensionality, degree of resolution).

Methodologies

Jacob (1999)[1] classifies CTMs as Eulerian/"box" or Lagrangian/"puff" models, depending on whether the CTM in question focuses on [1]

  • (Eulerian) "boxes" through which fluxes, and in which chemical production/loss and deposition occur over time
  • (Lagrangian) the production and motion of parcels of air ("puffs") over time

An Eulerian CTM solves its continuity equations using a global/fixed frame of reference, while a Lagrangian CTM uses a local/moving frame of reference.

See also

Examples of Eulerian CTMs
TCAM is a multiphase three-dimensional eulerian grid model (as opposed to lagrangian or other modeling methods). It is designed for modelling dispersion of pollutants (in particular photochemical and aerosol) at mesoscales (medium scale, generally concerned with systems a few hundred kilometers in size).[3]
TCAM was developed at the University of Brescia in Italy.[4]

Examples of Lagrangian CTMs

Examples of Semi-Lagrangian CTMs

Examples of ozone CTMs

Notes
  1. Jacob, Daniel (1999). Introduction to Atmospheric Chemistry (1st ed.). Princeton University Press. pp. 75–85. ISBN 0-691-00185-5.
  2. Horowitz, Larry W.; Stacy Walters; Denise L. Mauzerall; Louisa K. Emmons; Philip J. Rasch; Claire Granier; Xuexi Tie; Jean-François Lamarque; Martin G. Schultz; Geoffrey S. Tyndall; John J. Orlando; Guy P. Brasseur (2003). "A global simulation of tropospheric ozone and related tracers: Description and evaluation of MOZART, version 2" (PDF). Journal of Geophysical Research. 108 (D24): 4784. Bibcode:2003JGRD..108.4784H. doi:10.1029/2002JD002853. Retrieved 2008-06-08.
  3. Emetere, Moses Eterigho; Akinlabi, Esther Titilayo (2020). Introduction to Environmental Data Analysis and Modeling. Lecture Notes in Networks and Systems (No. 58). Springer. p. 18. ISBN 978-3-030-36207-2. Retrieved January 19, 2022.
  4. ESMA (Environmental Systems Modeling and Assessment) group of University of Brescia

See also
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