2022 Volume 100 Issue 3 Pages 555-573
We applied tracer transport simulations using the Taiwan vector vorticity equation cloud-resolving model (TaiwanVVM) to evaluate the effects of the local circulation associated with the lee vortex and the planetary boundary layer development on the transport and accumulation of the pollutants on a diurnal time scale in central Taiwan. The wind directions of crucial synoptic northeast monsoon are idealized as the initial conditions of the simulations to examine the impact of the lee vortex on the pollutant transport. The primary local nontraffic emission sources are taken as the tracer emission sites so that the experiment results could be a good proxy of the realistic scenarios. With the local circulation over complex topography being resolved explicitly, the impact of the boundary layer development on the tracer transport of the Puli basin is discussed. The simulation results clarify the contribution of the sea breeze and the lee vortex to the tracer transport in central Taiwan. We conclude that the high tracer concentration at Puli at night is due to the tracer being trapped by the thinning of the mixed-layer depth in the evening. The sensitivity of the local tracer transport to the change of the synoptic wind direction shows that under northeasterly due east (due north) environment, the pollutant transports from the southern source (northern source) of central Taiwan are most likely to induce a high concentration in Puli at night. This is the first study to distinguish the contribution of the sea breeze and the lee vortex in pollutant transport in Taiwan. The results obtained from idealized experiments provide the possible mechanism of pollutant transport, which could be taken as an insight to interpret the observations and guide the design of the field experiment to further establish the fundamental principles of the pollution transports in central Taiwan.
