Modelling Hourly Atmospheric Stability and Mixing Height Using Metrological Surface Data

Abstract

Atmospheric stability and surface boundary layer or Mixing Height (MH) are essential parameters in modeling of transport and diffusion of pollutants in the atmosphere. The thickness of mixing layer, plume rise from stakes and dispersion coefficients are depending mainly on the category of atmospheric stability at the time of estimation. In this study the Auxiliary Meteorological Model is used to estimate hourly atmospheric stabilities and heights of mixing layer using routinely measured metrological data in Assiut city; Egypt. The model determines Pasquill-Gifford atmospheric stability categories using observations of wind speed, incoming solar radiation, cloud cover and daytime. The results showed that the dominant category in day hours is the stability A especially in Summer and Fall seasons, while in the dark hours the dominant is the very unstable condition (stability F). For the height of mixing layer, 26% of the estimated values were less than 1500 m at stability A. While 53 % at stability B, 77% at stability C, 94% at stability D, 100% at stability E, and 100% at stability F were less than 1500 m. The main conclusion from this research is that the thickness of mixing layer is very small during dark hours for long periods thus increase the levels of pollutants on the ground surface. Therefore, industrial plants should decrease its activity during night hours as possible as they can or at least working with the minimum load of production.