| Abstrakt: |
Despite the importance of the boundary layer mixing height (MH) in air quality, its properties have not been thoroughly studied in the metropolitan area of Arak. This study used the air pollution model (TAPM) to compare the daily meteorological conditions in this layer on a monthly scale in the study area. Therefore, the vertical stratification of the potential temperature, turbulence kinetic energy (TKE), and horizontal wind speed (WSPD) were investigated with regard to the minimum and maximum MH values. According to the results, the maximum and minimum MH values (4849 m and 22 m) occurred on June 3 at 17:00 and October 3, 2015, at 04:00, respectively. In addition, the highest MH values were observed in June and July, whereas the lowest ones were recorded in November and December. Moreover, the air pollution level was maximal (1100 µg/m3) in June near the chimney of AzarAb Factory. The maximum MH value was less than 700 m in December. Also, due to the Arabian subtropical high-pressure system over Iran, the MH value in summer was less than in spring. Analyzing the vertical stratification of the potential temperature showed further severe vertical changes in the minimum MH value compared to the maximum one. During winter and autumn, the MH value was decreased by cooling of the Earth's surface and energy loss. Also, due to instability, the level of air pollution in the city was lower during the day and became maximal overnight, especially before sunrise. Finally, the gradual temperature rise increased the MH during the spring. Despite the unstable layer in this season, the air pollution level decreased as the north–south flows enhanced in the Middle East and West of Iran where Arak is located. [ABSTRACT FROM AUTHOR] |
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