ATMAS: a three-dimensional atmospheric transport model to treat multiple area sources

ATMAS, an atmospheric transport computer model, estimates the concentration of gaseous species emitted from multiple area sources. It can handle space- and time-varying wind fields, first-order chemical transformations, ground deposition, and inversion effects. The model presented here is based on the three-dimensional advection-diffusion equation to describe atmospheric transport. ATMAS solves this equation and calculates the concentration levels using the particle-in-cell method. The model calculates short-term (hourly) average concentrations over periods ranging from a month to a year; it can also calculate longer averages by varying the averaging time. We present a demonstration of the model, along with the output of the computer code. Output from the code typically includes isopleth maps showing the calculated concentration levels and the probability with which given thresholds or standards are exceeded during the simulation period.