| چکیده انگلیسی مقاله |
Ozone in the atmosphere serves as a greenhouse gas and a shield against ultraviolet radiation, making it crucial for maintaining ecosystem balance and promoting human health. Variations in its levels can adversely impact climate change and air quality. Therefore, monitoring ozone concentrations is vital for creating effective environmental policies and strategies to mitigate these impacts. For this purpose, MERRA-2 data was used from 1980 to 2019. This study aims to understand the variations in ozone levels across different regions and seasons and is comprised of two main parts. First, we analyzed spatiotemporal variations in ozone in Iran’s atmosphere. We explored how ozone levels change throughout the year and across different geographical locations. We found that the highest ozone levels occurred during spring (May), whereas the lowest levels were observed in autumn (October). Geographically, the highest ozone concentrations are observed in the northern and northwestern regions of Iran, while the lowest levels are found in the southern areas. These variations undergo monthly fluctuations influenced by various factors. In the cold season, ozone concentration is primarily a function of latitude, whereas, in the warm season, the impact of altitude becomes significantly more pronounced than latitude. The annual ranges of ozone change were 294 and 354.47. Notably, the total amount of ozone in Iran’s atmosphere exhibited overall negative annual, seasonal, and monthly trends. This trend was particularly pronounced during the cold months, with statistical significance observed in winter (α=0.01). Spatially, the northwestern region of Iran, extending to its central side, exhibited a significant trend, whereas other areas showed a non-significant negative trend. This can contribute to a better understanding of ozone dynamics in Iran and provide valuable insights for policymakers and researchers working on climate change mitigation. Extended Abstract 1-Introduction Environmental sustainability refers to the continuous preservation of natural resources and the reduction of environmental changes to maintain a balance between human activities and the environment, ensuring sufficient resources remain for future generations (Morelli, 2011). Among these, ozone (O3) is a significant greenhouse gas in the atmosphere (Kiehl et al., 1999) with a concentration of 0.0012% (Kerr & McElroy, 1989), produced as a result of chemical reactions and unintended compounds in the Earth's atmosphere. After carbon dioxide (CO2: 1.82 ± 0.17 Wm-2) and methane (CH4: 0.48 ± 0.05 Wm-2), this gas ranks third in greenhouse effects with a radiative forcing of 0.2 ± 0.4 Wm-2 (Heue et al, 2016; Hartmann et al, 2013) and acts as a protective layer against ultraviolet radiation from the sun. Therefore, changes in this gas will have significant consequences for humans, plants, and animals. Existing studies have mostly focused on tropospheric ozone in large cities such as Tehran, and there is a research gap regarding the spatial and temporal distribution of total atmospheric ozone in Iran. This study, aiming to fill this gap, monitors regional ozone levels at different time scales (monthly, seasonal, and annual) and examines its changes using non-parametric and Sen's slope methods to contribute to maintaining environmental sustainability. 2-Materials and Methods The study area is the country of Iran, with an area of approximately 1,648,195 square kilometers, located between latitudes 24° and 40° North and longitudes 44° and 64° East. As mentioned earlier, the purpose of this study is to investigate the spatiotemporal variations of total ozone over Iran. In this regard, data from NASA’s Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) were used. NASA's MERRA-2 reanalysis data is the latest product from NASA's Global Modeling and Assimilation Office (Koster, et al., 2015). To investigate the temporal variations of total atmospheric ozone over Iran based on the cells present within Iran's extent, two methods, Mann-Kendall and Sen's slope estimator, were employed. 3- Results and Discussion This study has two parts: a spatiotemporal analysis of ozone and an analysis of its temporospatial changes. Based on the results of the first part, it was found that the average ozone level in Dobson units is about 286.62, with the minimum average occurring in October (270.02) and the maximum in March (308.39). Geographically, the highest ozone concentration is in the north and northwest of the country, and the lowest ozone level is related to the southern half of Iran. More precisely, the lowest levels in these areas are observed in the southeastern borders of Iran and also in low-lying areas such as the Jazmourian depression. In general, the spatial distribution of total atmospheric ozone over Iran has an increasing trend from south to north. These changes fluctuate monthly under the influence of various factors. In the cold season, ozone concentration is mainly a function of latitude, while in the warm season, the effect of altitude is much greater and more pronounced than latitude. The amount of ozone decreases at higher altitudes. Zhou and Yue-juan (2005) also point to the presence of low ozone over the Iranian plateau during the summer season. And more importantly, the ozone deficiency in the Iranian plateau is greater than that of the Tibetan plateau. Chevalier et al. (2007) point to the role of altitude in changes in ozone levels. In general, at lower altitudes, local chemical and physical processes have a greater impact on ozone levels, while at higher altitudes, large-scale atmospheric processes are more influential. The temporospatial changes of the study showed that the range of annual ozone variation is between 294 and 354.47 Dobson. Other findings showed that in the overall amount of atmospheric ozone over Iran, a negative trend is observed on annual, seasonal, and monthly scales. This research showed that stratospheric ozone fluctuations have a strong relationship with sunspots, and numerous studies have confirmed this connection. Also, research shows that global ozone changes by an average of about 2% during solar maximum and minimum periods. In addition, volcanic eruptions such as Mount Pinatubo and El-Chichon have also significantly affected the stratospheric composition and ozone levels. The ozone trend in the cold period (months) is generally more pronounced and statistically significant in the winter season. Spatially, the northwestern areas of the country to the central part of the country have a significant negative trend, and other areas show the same negative trend but are not statistically significant at any level. The findings of this research are consistent with the results of studies by Raispour and Asakereh (2018), which were conducted using satellite data received from the Giovanni website. 4- Conclusion This study is the first spatio-temporal analysis of total atmospheric ozone changes over Iran using MERRA-2 database data. The results show that ozone levels generally decrease from north to south and northwest to southeast, with the lowest values in southern areas such as Sarbaz and Baft. Also, the temporal behavior of ozone shows annual fluctuations and its overall trend is negative, especially during the cold periods of the year. These changes are influenced by geographical and temporal factors, and appropriate management is essential to maintain environmental sustainability |