تحلیل تغییرات مکانی و زمانی عمق اپتیکی هواویزهای غبار مناطق مختلف استان کرمان در 23 سال گذشته

هواویزهای غبار اثرات نامطلوبی بر سلامت عموم، کیفیت هوا و محیط‌زیست دارند و پایش مستمر تغییرات زمانی-مکانی آن‌ها در مناطق مختلف به‌ویژه مناطق خشک و نیمه‌خشک حائز اهمیت زیادی است. بر این اساس، پژوهش حاضر باهدف تحلیل مکانی و زمانی هواویزهای غبار در استان کرمان انجام شد. پس از اعتبارسنجی داده های عمق اپتیکی هواویزهای غبار بر مبنای داده های مشاهداتی دید افقی، روند تغییرات بلندمدت (2022-2000) آن‌ها در مقیاس های زمانی مختلف با استفاده از آزمون من-کندال بررسی شد. بر اساس الگوی توزیع فضایی هواویزها مشخص شد که کیفیت هوای نیمه شرقی در ماه های اسفند و فروردین پایین‌تر از سایر نواحی استان بوده این در حالی است که در نواحی مرکزی، آلودگی هوا کمتر و کیفیت هوا مطلوب‌تر بوده است. نتایج حاصل از آزمون من-کندال نشان داد که در خرداد و آذر، روند تغییرات عمق اپتیکی هواویزهای غبار در بیش از دوسوم استان کرمان، کاهشی غیر معنی‌دار بوده است (z>-1.96). این در حالی است که در آبان و اردیبهشت، نیمی از استان و در سایر ماه‌ها بیش از دوسوم استان، تغییرات افزایشی هواویزها را در 23 سال گذشته تجربه کرده‌اند. یافته‌ها همچنین نشان داد که استان کرمان در تیر و فروردین بدترین شرایط را ازنظر حضور آئروسل‌های جوی داشته زیرا عمق اپتیکی آن‌ها در بیش از 87% مناطق استان به بیش از 5/0 رسیده است. در مقیاس فصلی، حدود 70 درصد استان در فصول بهار و پاییز و بیش از 95 درصد استان در فصول تابستان و زمستان با روند تغییرات افزایشی هواویزهای غبار ناشی از وقوع پدیده گردوغبار مواجه بوده اند. در مقیاس سالانه، همه مناطق استان کرمان، روند افزایشی هواویزها را در دوره آماری موردمطالعه تجربه کرده‌اند که این تغییرات در شهرستان‌های غربی بیشتر از سایر شهرستان‌های استان بوده است (z>+1.96).

analysis of the spatial and temporal changes of the dust aerosols optical depth across different regions of kerman province in the last 23 years

1- introductiondust aerosols have adverse effects on public health, air quality, and the environment; therefore, continuous monitoring of their spatio-temporal changes in different regions, especially arid and semi-arid regions, is very important. considering the vast spatial extent of kerman province, the inappropriate distribution of air pollutant measurement stations, a number of synoptic stations, as well as the large area of the province and the different climatic and biological diversity; the use of remote sensing techniques and especially the use of aerosol optical depth (aod) index of the modis sensor can be one of the appropriate tools to analyze and investigate the trend of temporal changes and the pattern of spatial distribution of dust particles in different regions of this province. this study has been carried out with the main purpose of analyzing the changes in dust aerosols based on the average monthly, seasonal and annual values of aerosol optical depth in different regions of kerman province during the period from 2000 to 2022, so that while knowing the state of these changes, the high-risk areas of dust production in recent decades should also be identified.2-methodologyin the present study, the modis sensor aerosol optical depth index product (mcd19a2) was used to analyze the trend of changes in dust aerosols in different regions of kerman province. in order to validate this product, the average daily horizontal visibility recorded on the days of dust events was used. the data related to the mcd19a2 satellite product was downloaded through programming in the google earth engine environment for different cities of kerman province in the period from 2000 to 2022. after filtering the dusty days (aod>0.5), the average values of the mentioned index on monthly, seasonal and annual time scales were calculated separately for each region. the mann-kendall test was then used to analyze the temporal changes of the optical depth of dust aerosols in different regions of kerman province. 3- results based on the spatial distribution pattern of the air quality, it was found that the air quality of the eastern half in march and april was lower than other areas of the province, while in the central areas, the air pollution was less and the air quality was more favorable. the results of the mann-kendall test showed that in june and december, the trend of changes in the dust aerosols optical depth in more than two thirds of kerman province had a non-significant decrease (z>-1.96). this is why in november and may, half of the province and in other months more than two-thirds of the province have experienced incremental changes over the last 23 years. the pattern of long-term average spatial changes of the optical depth of aerosols on a seasonal scale showed that kerman province was more affected by aerosols in the spring and summer seasons. maximum dust pollution has occurred from raver to rigan, jiroft to manojan, sirjan and anar cities. the mentioned areas in the cold seasons of the year have also experienced the worst conditions in terms of the presence of aerosols, but their concentration has been significantly lower compared to the warm seasons of the year. the results of the mann-kendall test showed that 75% of the cities of kerman province have faced an increasing-insignificant trend of spring dust events, which has led to an increase in the concentration of aerosols. in summer, these changes were increased in more than 95% of the province’s regions, and the most changes were observed in anar, baft, fahraj, kohnouj, kohbanan, orzuiyeh and rafsanjan. although in the fall season, about 25% of the regions of the province had a decreasing trend and about 4% had no particular trend, but in more than 70% of the regions of kerman province, the trend of changes in dust aerosols was an increase, and among the regions with a positive trend, the cities baft and jiraft had the worst conditions (z>1.96). the remarkable result is the rising trend of dust and dust aerosols in all regions of kerman province during winter, particularly in the cities of anar, anbarabad, baft, faryab, ghaleganj, manojan and rabor. although anbarabad, baft, orzuiyeh, shahrbabak and sirjan exhibit a stronger annual increase compared to other areas, the rise in aod changes is evident throughout the province. this 23-year trend indicates that kerman has not experienced favorable conditions, highlighting the increasing frequency of dust events in this desert region.4- discussion & conclusionsbased on the findings of the analysis of the temporal changes of dust aerosols; the western cities of the province have become more sensitive to the phenomenon of wind erosion compared to the past. this can be a serious threat to the residents of these areas. on the other hand, the increasing trend in the southern and eastern regions highlights the intensification of dust events, contributing to the decline in air quality in the province over recent decades. considering the intensification of the phenomenon of wind erosion and dust storms in many areas of kerman province, it is necessary to control this phenomenon in order to increase the health security of the residents of the affected areas. although the awareness of the spatial and temporal changes of dust aerosols has led to an increase in our understanding of the phenomenon of wind and dust erosion in the province, but in order to prevent, control and reduce the risks caused by the occurrence of this destructive environmental phenomenon, it is necessary to identify the main driving factors of these changes that are suggested to be investigated separately for each city in future researches.