Synoptic Analysis of Effective Ridge Positioning on Air Pollution Over Five Selected Metropolises of Iran

Today, air pollution has tightened the air for the residents of metropolises. Air pollution is one of the most harmful pollutants for the environment especially for humans. In this study, based on daily data, concurrent and widespread air pollution in five selected metropolises in the northern half of Iran, including Tehran, Mashhad, Tabriz, Isfahan, and Rasht, was investigated to design and analyze synoptic patterns related to the atmospheric ridges affecting them. For this purpose, the beginning, peak, and end days of concurrent and multi-day pollutants (pollution wave) were identified and for each of them, the effective atmospheric ridge position was determined. The first results showed that 107 air pollution waves with simultaneous characteristics occurred during the period 2017 to 1400. Of these, 14 waves have been widespread. Synoptic patterns showed that when the same height curve of 5825 geopotential meters, along with other curves in the northwest of the African continent, formed a subtropical atmospheric ridge, the widespread air pollution in the westernmost metropolis of Iran, Tabriz began. When this ridge reaches Iran, air pollution covers four of the five selected metropolises of Iran, and then, as the ridge reaches Pakistan, the air conditions face a clean state and a wave of pollution is coming to an end. In total, the East-ward movement of the ridge axis during the three days of the beginning, peak, and end of air pollution was evident on three territories including Iraq, Iran, and Pakistan, respectively. These three situations confirmed the coordinated behavior of the atmospheric pattern of the ridge with concurrent and widespread air pollution for residents of five metropolises of Tabriz, Rasht, Tehran, Isfahan, and Mashhad.

 Today, we are witnessing population increase, the growth of the techniques, the rapid expansion of cities, and the manipulation of the earth's ecosystems by humans. These have caused air pollution, especially in the metropolis, to become an important bottleneck for the population living and active in them. The atmosphere is a huge system of dynamic and interrelated components.  These two characteristics have so far caused natural pollutants such as particles and ash from volcanoes and human pollutants such as aerosols and soot in urban and industrial environments during the upward and downward movements of the atmosphere and mechanisms such as precipitation have been cleared from the atmosphere or have the opportunity to spread and disperse gradually. What has become a serious hazard today is the indiscriminate increase of pollutants and their concentration in industrial areas, including in metropolises.

This study was conducted with an environmental approach to circulating. To design and analyze synoptic patterns of concurrent and widespread air pollution in five selected metropolises of Iran, including Tabriz, Rasht, Tehran, Isfahan, and Mashhad. The daily air pollution data for six pollutants from air pollution monitoring stations were collected from the Iranian meteorological organization. These six pollutants include carbon monoxide, ozone, nitrogen dioxide, sulfur dioxide to PM10, and PM2.5 aerosols between 2017 and 2021. Calculation of Air Pollution Measurement (AQI) for each of the six pollutants and based on valid air quality indicators, the polluted days were retrieved in each of the mentioned metropolises. Determination of concurrent and continuous days of air pollution from sequential and asynchronous days provided the possibility of determination of concurrent and widespread waves of air pollution. Widespread and simultaneous waves of air pollution were defined as waves that have four characteristics:
There should be a report of pollution from one of the metropolises and generally the westernmost metropolis of Tabriz.
During the following days, other metropolises in the center and east of the country have been involved in pollution.
During one day of the continuous days of pollution, the highest number of metropolises (generally out of 5 metropolises of 4 ones) have shown pollution.
During the following days, the frequency of contaminated metropolises should be reduced to zero.
To achieve the aim of the study, the daily weather maps from the middle level of the atmosphere were studied for the days of air pollution waves.
 By accessing daily air maps at sea level and the middle level of the atmosphere, the dominant location of pressure systems including effective ridges was drawn on base maps in the form of synoptic patterns for the beginning, peak, and end days of widespread air pollution. The purpose of this positioning was to match the eastward shift of southern ridges along the geographical orbits during three simultaneous conditions in the pollution index values for selected metropolises of Iran. These three conditions included the positioning of the effective ridge during the beginning, peak, and then end of the registration of contamination values.

The first results showed that the most polluted months for the five selected metropolises were December, January, and February, respectively. Meanwhile, the pollution behavior of the two metropolises of Tehran and Isfahan was closer to each other than other cities and had two peaks, one summer and one winter. The longest wave of pollution lasted 17 days and the shortest wave lasted 5 days of a total of 107 monitored pollution waves, 14 were of widespread characteristics. The prevalence of air pollution wave in this study was defined as air pollution in at least four cities out of five metropolitan areas at the same time. The design synoptic patterns showed that when the curve of 5825 geopotential-meters height is seen from the set of effective ridge curves in northwest Africa, we can expect the beginning of widespread air pollution in Tabriz metropolis and then the eastern cities up to Mashhad. Positioning patterns showed that with the reach of the ridge on Hejaz land, pollution became widespread and since then, the pollution wave in the east of the country has subsided.  Also, the ridges in southern latitudes had a longer range (more orbital elongation) than the types monitored in northern latitudes. The orbital elongation of the ridges in the southern half of Iran shows that the cities of the southern part of Iran have a hidden and alarming potential for the occurrence of durable pollutants in the event of expansion of industries and sources of urban and industrial pollutants.

The co-occurrence of widespread air pollution in selected metropolises of Iran with the apparent shift of subtropical ridge toward the east from Africa indicates the high potential of Iran's atmosphere, especially in the southern regions for increasing traffic and industrial pollutants in urban space. In other words, when the synoptic aspect dominates in a climate hazard, planners should be more concerned with preventive and long-term measures than curative and short-term ones. It means the widespread air pollution of Iranian metropolises has a synoptic aspect and relating to the nature of Iran's climate, which has atmospheric stability for most days of the year, increasing access to clean energy is essential.