Influences of initial conditions and boundary conditions on regional and urban scale Eulerian air quality transport model simulations

Influences of initial and boundary conditions were quantified by analysis of a simplified governing equation followed with a tracer and O₃ simulations using a three-dimensional air quality transport model. The analytical solution derived from the governing equation indicated that the impacts of initial conditions on a given site decrease with simulation time and significantly affect the species concentrations before the arrival of the boundary conditions. Boundary influences, which decrease during the downwind transport, are significant to a selected site when the arrival time of boundary condition is short and the species lifetime is long.

Non-reactive tracers and O₃ were then added to SARMAP Air Quality Model (SAQM), a three-dimensional transport model, and the results showed that tracer lifetime and arrival time determine the boundary influences on a given site consistent with the analysis obtained from the governing equation. Moreover, boundary conditions followed initial conditions to affect the calculated ozone concentrations at a given site and the influences are proportional to the magnitude of the prescribed boundary conditions, arrival time, and are more obvious at local nighttime. When the arrival time is 15 h, an average of 64% of initial ozone boundary conditions will contribute to the calculated ozone concentrations. For arrival times of 23, 20, and 7 h, the ratios are 26%, 34%, and 79%, respectively. This study indicated that the derived analytical solution could be used by air quality modelers in estimating the boundary influences as long as the species lifetime are known.