چكيده لاتين :
Abstract:
According to the statistics of the Organization of the Environment, a total of 48 days of air pollution exceeds the admissible threshold (AQI more than 150) for the three months of the year. These days coincide with the time when Tehran's inversion reaches its maximum stability. The purpose of the present study was first to determine the height of air pollution in Tehran on the days when pollution exceeds the permissible limit. It also aims to study the pressure and temperature masses of such days, considering the geographical and topographic conditions, and finally to identify the best of these cells for theoretically possible air turbulence. The results of this study, based on Tehran temperature and pressure data over a 15-year period (2003-2017), show that the highest elevation of Tehran inversion does not exceed 1800 meters on polluted days. Only within 6 days of whole days beyond the admissible threshold, temperature and pressure cells with the highest Newtonian mass are formed. The center of such cells shows a pressure difference of 32 milligrams in November, 7 milligrams in January, 100 milligrams in December, as well as a temperature difference of 1.1 degrees in November, 4.4 degrees in January, and 1.9 degrees in December. Based on the results and topographic conditions as well as the cell adaptation to such conditions, it seems that theoretically, it is possible to artificially create air turbulence in Tehran to mitigate the contamination amount.
Extended Abstract
Introduction
Tehran is one of the largest and the most crowded cities that suffers from air pollution. On some days of the year, the amount of contaminating and pollution elements increases so much that breathing is very difficult for inhabitants. The Air Quality Index (AQI) varies over the course of a year in Tehran. During autumn and winter, Tehran becomes more polluted. Atmospheric temperature inversion worsens air pollution during that period. The two factors of climate and topography are affecting air pollution in Tehran. These two factors are emphasized in this research to look for a way to eliminate or at least decrease the pollution of Tehran's air. This research focuses on vertical and horizontal exchanges via atmospheric mixing by defining the good conditions for instability during the inversion periods in Tehran. If there are suitable mixing conditions (identified with cells of pressure and/or temperature), we could define the best status for instability. There is a need to know the differences between temperature and pressure that give rise to air turbulence.
Methodology
Firstly, the pressure and temperature maps were drawn at different levels of the atmosphere. Further, based on these maps, the levels that had the most number cells of pressure and temperature with the most gradient were selected. This revealed the degree of differences in temperature and pressure that cells should have to create instability. We used the synoptic stations and the air pollution testing stations as well as Google Earth, Arc GIS, Surfer, and Voxler software
Discussion
In the first step, we find the days when the AQI (Air Quality Index) was greater than 150 as dangerous days of pollution from 2003 until 2017. In order to calculate the average inversion level, Radiosonde data were used. The height of the inversion phenomenon in Tehran is not the same in the target months (January, November, and December). The highest inversion height in the target months is 1800 m and the lowest is 1300 m. Exceedance of the AQI index or the pollution crisis threshold does not cover all areas of Tehran in the target months. That is, while some districts of Tehran experience higher pollution than the thresholds, others do not. During December, the expanse of pollution in Tehran is wider than other target months.
Next, based on the determined inversion levels, the zoning maps of pressure and temperature on critical days of pollution were drawn in the target months. From among them, maps containing temperature and pressure cells were selected, then a matrix was prepared for all cells in the selected maps and their Newtonian mass was calculated. This matrix represents the cells that have the gradient because the two factors of cell difference and distances play a major role in their triggering. Finally, for each month, two temperature and pressure cells with the highest Newtonian mass were selected.
In order to investigate the effect of topographic terrains on temperature and pressure cells, and to further understand the location of these cells, the temperature and pressure cells were overlain on the topography of the area. For this purpose, a 3D map of the area’s heights was plotted, and the synoptic stations, pressure, and temperature cells overlapped for analysis and investigation.
Conclusion
The following results were obtained by drawing and examining the pressure and temperature maps:
1) There are two cells in the November temperature map at Imam Khomeini Airport Station and Mehrabad Station. Imam Khomeini's cell is located at an altitude of 990.2 meters near the low elevation range of southern Shahriar. Mehrabad cell is located at an elevation of 1190 meters and in the easterly part of the southern Alborz Mountains.
2) The temperature maps of January with two cells of geophysics and Shemiran are 1423.8 m and 1548.2 meters, respectively. The two formed cells are located in the recesses of the southern slope of the Alborz Mountains, and it may be noted that the confinement of cell formation zones may influence the formation of these temperature cells.
3) The December temperature map contains two cells of geophysics and Shemiran, which are located at altitudes of 1423.8 and 1548.2, respectively. These two cells are also located in the indentation of the southern slope of the Alborz Mountains.
4) On the map of November pressure difference, two cells of Chitgar at 1305.2 height and Imam Khomeini airport cell at 990.2 height are located. The Chitgar Cell lies on the southern slope of Alborz, where the heights have advanced, and the Imam Khomeini Airport cell is near the low-lying slopes south of Shahriar. The formation of these pressure cells at the sites mentioned may be affected by the air currents in the area. These currents, due to the advance of the southern slopes of the eastern highlands, divert the surface winds of these currents to the southern plains and increase the relative wind velocity at these points.
5) The January pressure difference map shows two cells of Mehrabad with a height of 1190.2 and Chitgar with a height of 1305.2 meters. The two cells are located on the eaves of the southern Alborz Mountains.
6) December pressure maps showed two cells of geophysics and Mehrabad. These two cells were located at 1423.8 and 1190.2, respectively. These two cells are located on the northern elevation of Tehran. In fact, this part of the southern slope of Alborz is indented, and this retreat can be effective in winds and existing cells.
According to the obtained results, among all days that the AQI passes the threshold, only in 6 days, temperature and pressure closed cells with the highest Newtonian mass are formed. The center of these cells shows a pressure difference of 32 milligrams in November, 7 milligrams in January, 100 milligrams in December, and the temperature difference of 1.1 degrees in November, 4.4 degrees in January, and 1.9 degrees in December.
Generally, considering the formed cells by the temperature and pressure difference and the gradient between them as well as the difference in height between the cells and their location and pointing out that the local winds cause the difference of temperature and pressure, it seems that, theoretically, it is possible to create artificial air turbulence in Tehran within the study area to control the contamination amount. Knowledge of the conditions in the study area is natural in this study and there is no uniformity pattern for all areas in the subject area. This study was conducted only for a limited period of 15 years (from 2003 to 2017) in the study area of Tehran province and also all analyses were performed on the basis of statistics measured in synoptic stations in this area. It should be emphasized that all reviews and results are based on this range and the data and cannot be generalized.
