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).
TCAM (Transport Chemical Aerosol Model; TCAM): a
mathematical modelling method (computer simulation) designed to model certain aspects of the Earth's atmosphere. TCAM is one of several chemical transport models, all of which are concerned with the movement of chemicals in the atmosphere, and are thus used in the study of air pollution.
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]