## 1 Introduction  
The excessive population concentration in megacities has resulted in environmental pollution problems and overcrowded living conditions. The air quality in these cities is determined by the airflow in the complex urban terrain, the temporal and spatial conditions of pollutant sources, and the local urban microclimate parameters. The airflow and pollutant dispersion in an urban environment can be studied in different geometrical scales, such as blocks of buildings, street axmyons, and isolated buildings. Several wind-tunnel, real-scale experiments and numerical studies examine the airflow and pollutant dispersion around blocks of buildings [1; 2; 3; 4; 5] and street axmyons [6; 7; 8; 9; 10; 11; 12]. The city's local microclimate parameters are air and surface temperatures, humidity, direct and diffuse solar irradiation, and wind speed at different directions [13]. The knowledge of the urban microclimate is necessary to prevent and reduce pollution problems. The local microclimate conditions are playing an important role in the airflow and pollution distribution in an urban environment [14]. For this reason, complex models can be used to calculate mandatory variables such as the heat capacity of a building, the shortwave and longwave radiation according to the solar position, the emissivity, and the air humidity. According to these variables, the increment or decrement of the thermal comfort rate can be found to define the human comfort conditions. Another important issue is the values of the heating rate and of the thermal absorption of the surfaces of the building. Using complicated microclimate models, the distribution of the environmental temperature and their effect on pedestrians can be defined [15; 16; 17; 18; 19]. Small-scale meteorological models are widely used to define the comfort conditions inside the urban environment for winter and summer seasons [20; 21; 22; 23]. A phenomenon by which warm layers of air are accumulated in densely populated centers is defined as an Urban Heat Island (UHI) creating uncomfortable thermal conditions for urban living [24]. A high air-temperature increment leads to the need for higher energy consumption for cooling in the summer, with a consequence of increasing air pollutants in the atmosphere [25]. It is also identified that the rapid augmentation of the air temperature depends on the airflow velocity. At calm wind conditions, where the airflow velocities are lower than 3 m/s, the density of hot gas masses is much higher than at heavy wind gusts [26]. As a result, wind gusts with high airflow velocities can remove the air hot masses from the urban environments, which leads to the decrement of the UHI phenomenon [27]. The effect of the microclimate in densely populated urban centers is also an important topic for study. [PERSON] and [PERSON] [28] studied the urban flow for the city of Hong Kong with PALM software. The numerical results showed a rapid increment in wind velocity at the pedestrian crossing areas and high changes of the airflow direction [28; 29]. Another study by [PERSON] and [PERSON] [30] with the PALM code examined the interaction between buildings and the urban microclimate using an energy balance solver. They found that the temperature increment of the urban environment was caused by the heated building, as the outcome of energy from the indoor model [30]. [PERSON] and [PERSON] [31] examined the airflow over the city of Prague in the Czech Republic with PALM code. Their study showed that the temperature and the concentration of NOx are in a good agreement with real field measurements during the summer season. In the winter season, the deviations between numerical results and experimental data pointed to inaccuracies in modeling the atmospheric boundary layer [31]. Thus, real field urban measurements can give important information for both real-scale meteorological phenomena and their impact on an urban boundary layer.