بررسی نقش الگوهای گردشی جو مولد آلودگی شدید هوا در شهر اصفهان

در این پژوهش جهت شناسایی نقش الگوهای گردش منطقه ای جو در رخداد آلودگی های شدید هوای شهر اصفهان، از روش تحلیل همدید ترکیبی استفاده شد. برای انجام پژوهش، از داده های ایستگاه های سنجش آلودگی هوا، داده های رقومی پروفیل جو، و خروجی های مدل پسگرد ذرات معلق (hysplit) در یک دوره 11 ساله (1395 1384) استفاده شد. نتایج نشان داد که چهار عامل و الگو در زمان رخداد شدیدترین روزهای همراه با آلودگی در شهر اصفهان در تراز میانی جو حاکمیت دارند. نتایج حاصل از بررسی مقادیر psi در هر الگو نشان داد که به ترتیب از الگوی یک تا چهار مقادیر شاخص 221، 238.6، 203 و 281 است. از شرایط همدیدی می توان به حضور پرفشار جنب حارهای اشاره نمود که همزمان با لایه وارونگی دمایی در ترازهای زیرین جو و وردسپهر میانی همراه شده است. تقویت تاوایی منفی در بالاتر از تراز 700 هکتوپاسکال و وجود یک همگرایی سطحی ادامه یافته تا تراز یاد شده سبب شده تا ماهیت جو تابستانه به وضوح در رخداد آلودگی در این شهر مشهود گردد که با وجود ناهنجاری های فوی این شرایط تقویت شده است. از طرفی خروجی مدل پسگرد ذرات معلق نشان داد که رخداد روزهای بسیار آلوده در شهر اصفهان را نمی توان در آلاینده های شهری همچون کارخانه های صنعتی اتومبیل ها و... جست بلکه با ورود ذرات معلق از مناطق مختلف سبب شده تا آلودگی از شدت بالاتری برخوردار باشد بدین صورت که هجوم ذرات معلق گردوغبار در تشدید این پدیده امری انکار ناپذیر است.

investigating the role of atmospheric circulation patterns in the severe air pollution in esfahan

the atmosphere is a dynamic system in which a large number of physical and chemical processes occur simultaneously. studying the dynamics and transmission of pollutants in the atmosphere using atmospheric patterns is one of the important topics in this field. atmospheric patterns simulate the occurrence of different processes within the atmosphere and their interactions. using an atmospheric model also requires comparing the results of the model with field and laboratory experiments. this helps in understanding the occurrence of chemical and physical processes in the atmosphere as well as evaluating the implementation of a suitable model. laboratory measurements provide valuable information while at the same time visualizing and describing atmospheric properties and atmospheric composition at specific time and space intervals. an atmospheric model provides a complete picture of the evolution of spatial and temporal variations in atmospheric pollutants at different altitudes. understanding atmospheric dynamics can be understanded by combining measurements and integrated modeling with using synoptic systems in periods with pollutated air. therefore, in this study, it has been attempted to analyze the atmospheric factors that cause severe pollution in esfahan and the relationship and mechanism of the atmosphere at the time of occurrence of this phenomenon. data and methods in this study, three datasets including pollution data recorded at air pollution stations, digital atmospheric data and high atmospheric stations were used. the air pollution data are from three stations of laleh square, azadi and bozorgmehr which were obtained from esfahan general environmental protection office. the pollutants include carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone and suspended particulate matter (pm10), which have been prepared and processed daily for a 12 year statistical period (1995 2005). to study atmospheric conditions were used re analyzed data from the national center for environmental prediction (ncep / ncar) include sea level pressure, geopotential height, vertical velocity (omega), wind orbital components (u), and meridian wind ( v) was used for different levels of atmosphere. the above atmospheric data were obtained from the university of wyoming site for the study days, including air temperature, dew point temperature, wind direction and intensity, and atmospheric stability and instability conditions (based on skew t curves). in this study, a lagrangian model with the capability of tracking particle backward in different levels of atmosphere called hysplit was used to investigate the days associated with severe pollution. results and discussion the results show that the highly pollutated days of the city of esfahan can be explained by the four synoptic patterns. the occurrence of days with extremely severe pollution in esfahan, rather than being rooted in local factors, is due to the interaction of local conditions with atmospheric circulation at the regional scale. in other words, the city of esfahan will only experience extremely polluted days when the atmospheric circulation of the atmosphere provides conditions for increased concentrations of pollutants. the main causes of the occurrence of days associated with maximum contamination can be attributed to subtropical high latitude and its progression to higher latitudes. this circulation system contributes to the occurrence of highly polluted days on most days, either directly or in combination with other atmospheric systems. the role of local factors such as the formation of inversion layer and the increase of atmospheric thickness due to the dominance of high pressure systems in the region can also be considered to exacerbate the conditions. the use of suspended particle backward models and the study of atmospheric thermodynamic relationships have provided a deeper and more accurate understanding of the mechanisms dominating the occurrence of pollutants in esfahan.