Numerical Analysis of Air Pollution in a Combined Field of Land/Sea Breeze and Mountain/Valley Wind

Abstract

Air pollution in the presence of two types of local flows (i.e., land/sea breeze and mountain/valley wind) was studied by advection simulation of the cluster of hypothetical fluid particles, and transport/chemistry calculation employing a three-dimensional Eulerian model for 20 advected species and about 90 chemical reactions. Three-dimensional flow fields over the River Yahagi basin in Japan were estimated for 48 h using an observe method with routine wind observations. Those obtained showed characteristics of the combined local flows such that in the daytime sea breeze and valley wind tend to form one united flow with substantial wind velocity in the whole region and, in contrast land breeze and mountain wind during the nighttime form two separated circulating flows with a clear weak-wind area between the two local flow regimes. The results of the advection simulation of fluid particles and the transport/elements calculation using those flows as inputs elucidated how the features found in the diurnally varying, complex local flows contribute to produce characteristic time-variations of the concentrations of both primary and secondary pollutants. Among others, dynamics of NO₂, HNO₃, PAN, O₃, SO₂, and SO₄⁼ concentrations are discussed.