Simulation of atmospheric dispersion of airborne effluent releases at a tropical coastal site under sea-breeze circulation and internal boundary layer development

Abstract

In this study the impact of land–sea breeze circulation and internal boundary layer (IBL) on the atmospheric dispersion of airborne effluent releases at the tropical coastal site Kalpakkam is simulated using mesoscale model WRF and Lagrangian particle dispersion model FLEXPART. Simulations with WRF are conducted for typical days in different seasons, i.e., 3 May 2011 (summer), 20 Sep 2010 and 20 Jun 2011 (southwest monsoon). Two K-based non-local turbulence closures (YSU, ACM) and two TKE-based local closures (MYNN, MYJ) in WRF are tested for simulating the sea breeze and IBL. Observations from a 50-m meteorological tower, GPS Sonde, and a Doppler SODAR are used for validation. Simulations indicate that the synoptic flow largely influences the characteristics of the sea breeze at the site. Results show that the sea breeze is more predominant with early onset and it is characterized by deep inland penetration, strong horizontal and vertical winds and is associated with formation of a deep IBL relative to monsoon with opposing large-scale flow. The YSU non-local diffusion scheme and the higher order local TKE closure (MYNN) simulated the sea breeze and IBL characteristics in good agreement with observations. Dispersion simulations with a hypothetical tracer release using FLEXPART showed relatively high ground-level concentrations during IBL formation in the daytime and during stable off-shore flow condition in the morning time. The coupled mesoscale dispersion model could simulate the plume trajectory and buildup of concentrations during sea-breeze time by realistically simulating the winds and mixed-layer characteristics at the coastal site.