Simulation of mixing depths incorporating the urban heat island effect

The main objective of this paper was to establish the effect of anthropogen ic heat flux on the formation of mixing depth specially in urban areas. In this study an energy balance mixing depth model was developed for the simul ation of mixing depth incorporating the heat island effect. To demonstrate the effect of heat island, mixing depths were simulated under two condition s. Under the first condition, hourly gridded anthropogenic heat flux and va riant surface characteristics were considered, while under the second condi tion anthropogenic heat flux term was ignored and constant surface characte ristics were considered throughout the modelling domain. The release of ant hropogenic heat flux in the urban environment was found to be responsible f or the growth of the unstable layer in the lower atmosphere even during the night. This resulted in higher mixing depth values in urban areas compared to the surrounding countryside. The maximum differential surfaces sensible heat flux between urban and rural areas was estimated as 130 W/m(2). From the simulation of mixing depth, it was revealed that the maximum increment in mixing depth in urban areas was 300 m due to the heat island effect. Thi s increment in mixing depth in urban areas can provide an extra space for d ilution and mixing of pollutants.