The Comprehensive Air quality Model with extensions (CAMx) is an Eulerian photochemical dispersion model
that allows for an integrated one-atmosphere assessment of gaseous and particulate air pollution
(ozone, PM-2.5, PM-10, air toxics, mercury) over many scales ranging from sub-urban to continental.
It is designed to unify all of the technical features required of state-of-the-science air quality
models into a single system that is computationally efficient, easy to use, and publicly available.
The model code has a highly modular and well documented structure which eases the insertion
of new or alternate algorithms and features.
CAMx simulates the emission, dispersion, chemical reaction, and removal of pollutants in the
troposphere by solving the pollutant continuity equation for each chemical species (l)
on a system of nested three-dimensional grids. The Eulerian continuity equation describes
the time dependency of the average species concentration (cl) within each grid cell volume
as a sum of all of the physical and chemical processes operating on that volume.
The governing equations are expressed mathematically in terrain-following height (z) coordinates.
It considers a horizontal wind vector, net vertical entrainment rate, multiple vertical layers,
atmospheric density, and turbulent exchange (or diffusion).
The terms on the right-hand side represents horizontal advection, net resolved vertical transport
across an arbitrary space- and time-varying height grid, and sub-grid scale turbulent diffusion.
Chemistry is treated by simultaneously solving a set of reaction equations defined from specific
chemical mechanisms. Pollutant removal includes both dry surface uptake (deposition)
and wet scavenging by liquid precipitation (rain).