MODELLING THE DUST CONTENT OF THE ATMOSPHERE OF KARAKALPAKSTAN SOIL AEROSOL FROM DESERTS

ABSTRACT

The article considers the modeling of atmospheric dust in Karakalpakstan by soil aerosol from the desert territories of Ustyurt, Aralkum, Kyzylkum and Karakum.  The results of calculations of aerosol concentrations from April to October 2023 are presented. The Gauss model was chosen as the base model. Model calculations showed that the dust content of the atmosphere of the Lower Amudarya oasis in April, May, July, August and September exceeds the average monthly dust MPC established by the SanPiN of the Republic of Uzbekistan, respectively, by 300.3, 86.3, 88.1, 56, 49.2 µg/m³. According to the weather station, it was revealed that in the period of the greatest deflation from April to October, the northeast (26%) and northwest (24%) wind directions prevail. The greatest dustiness of the atmosphere is in the north-western and western regions, the least in the southern regions of Karakalpakstan.

АННОТАЦИЯ

В статье рассматривается моделирование запыленности атмосферы в Каракалпакстане почвенным аэрозолем с пустынных территории Устюрта, Аралкума, Кызылкума и Каракумов.  Представлены результаты расчетов концентрации аэрозолей с апреля по октябрь 2023 года. В качестве базовой модели было выбрано модель Гаусса. Модельные расчеты, показали, что запыленность атмосферы Нижнеамударьинского оазиса в апреле, мае, июле, августе и сентябре превышает среднемесячную ПДК пыли установленным СанПиН Республики Узбекистан, соответственно на 300.3, 86.3, 88.1, 56, 49.2 мкг/м³. По данным метеостанции выявлено, что в периоде наибольшей дефляции с апреля по октябрь, преобладают северо-восточное (26%) и северо-западное (24%) направления ветров. Наибольшая запыленность атмосферы в северо-западных  и западных, наименьшая – в южных районах Каракалпакстана.

Keywords: Atmospheric dustiness, dust storm, Lower Amudarya oasis, Southern Aral Sea region, aerosol concentration, mathematical model, wind regime.

Ключевые слова: Запыленность атмосферы, пылевая буря, Нижнеамударьинский оазис, Южное Приаралье, концентрация аэрозолей, математическая модель, ветровой режим.

Introduction. Atmospheric pollution is an important environmental problem in Karakalpakstan. A significant part of the pollutants is dust of both industrial and natural origin. In the conditions of the Southern Aral Sea region, the vast majority of atmospheric pollution occurs under the influence of natural sources of atmospheric dust (wind and convective removal), which, compared with industrial ones, have much larger spatial scales of influence, are less manageable and have a number of poorly studied aspects. It can be concluded that in this study, atmospheric pollution is a problem of dustiness in the Lower Amudarya oasis, surrounded on all sides by deserts and where the majority of the population of Karakalpakstan is concentrated.

The dustiness of the atmosphere is especially relevant for many countries of the world located in the desert zone, including Uzbekistan, whose vast territories are occupied by the Kyzylkum, Ustyurt, Aralkum and partially Karakum deserts. The relevance of the problem of atmospheric dustiness is evidenced by many publications, most of which are devoted to dust storms, which are the main natural source of dust (Fig.1).

Figure 1. Dust storms: a) Urgench, May 27, 2018; b) Nukus, May 27, 2018 (https://www.gazeta.uz/ru/2018/05/28/sand-salt/).

Cases of a dust storm with a tenfold excess of the dust MPC, as well as existing uncertainties in the mechanism of occurrence of a dust storm, require further in-depth studies of the problem of atmospheric dustiness [1].

Dust storm monitoring uses various methods that implement ground-based observations, satellite remote sensing and integrated approaches using mathematical modeling [2, 3, 4]. The primary methods of atmospheric dustiness research are the analysis of remote sensing data, the comparison of remote sensing data with statistics of weather station data and the state of the underlying surface [5].

In addition to Earth remote sensing data, state monitoring of atmospheric dust is carried out by ground-based measurements at weather stations, which are extremely unevenly distributed across countries (Fig.2) and often with a limited range of measurements, which presents a problem with the representativeness of the data [5].

Figure 2. The network of weather stations in Karakalpakstan (left) and Mongolia (right)

According to the data of the weather station, remote sensing of the earth and the results of modeling, the total mass of dust entering the Earth's atmosphere is estimated from several hundred to several thousand million tons per year [6, 7]. In addition to soil particles, the dust contains heavy metals, pesticides and microbes.

The most difficult task of monitoring the dust content of the atmosphere is the quantitative assessment of the 3D distribution of dust in the atmosphere, the solution of which is practically possible only by mathematical modeling methods. Ground-based monitoring is also important in the field of modeling as a source of numerous inputs and data for the ratification of model results.

Materials and Methods. It is important to clarify the factors and their contributions to the dustiness of the atmosphere, as well as their seasonal and interannual dynamics. Such a study of atmospheric dustiness is especially relevant for the Southern Aral Sea region, the main population of which lives in the Lower Amudarya oasis, surrounded on all sides by the Kyzylkum, Karakum, Ustyurt and Aralkum deserts (Fig.3), which are a source of large-scale atmospheric pollution during dust storms.

Figure 3. The Lower Amudarya oasis surrounded by deserts

The significance of the modeling of the dustiness of the atmosphere of the Lower Amudarya oasis described below is to obtain detailed spatially distributed information about air quality that is unattainable using standard measurement methods. In addition, this development allows us to identify patterns of temporary (seasonal, interannual) dynamics of atmospheric dust content, which are necessary both in the field of healthcare and in solving climatological and environmental problems of the Aral Sea region. 

We are developing a mathematical model to assess the complex effect of the above 4 sources on air dustiness. To implement this model, the entire calculation area was divided into elementary sites with a size of 25x25km. From the whole set of elementary sites of the calculation area, sub-arrays of sources   (Kyzylkum),  (Aralkum),  (Ustyurt) are formed,   (Karakum) and a sub-massif of the area of influence of these sources  (Lower Amudarya oasis).

The removal of dust from each  elementary site  is calculated using the Gaussian formula [8]

                    (1)

where  – dust concentration in the atmosphere (µg/m³) [9, 10, 11, 12, 13]. To calculate the parameters, the average monthly data on weather stations most closely located to the centers of dust removal were used [14].

Pasquill's formulas were used to calculate the coefficients of variance [15],

where:

The density and diameter of the particles are set from a set of the most common aerosol microparticles found in the Aral Sea region (table 1).

Table 1

The density and diameter of the particles are set from a set of the most common aerosol microparticles found in the Aral Sea region

According to formula (1), the spatial distribution of the dust concentration   from each elementary site of the  subarray source is calculated. Thus, the concentration of dust in the elements   from a given elementary site is determined in a particular month of the year with a given wind regime for it. The total dust concentration from the  source in the element   of the array   is determined by summing:

This algorithm is repeated for all source subarrays, as a result of which the total dust concentration in the elements of the array  is calculated:

Results and Discussion. Model calculations have shown that at wind speeds above 3 m/s, dust from the desert covers the entire Lower Amudarya oasis (Fig. 4).

Figure 4. The average monthly concentration (µg/m³) of dust from April to October 2023.

In the period of the greatest deflation from April to October, the north-eastern (26%) and north-western (24%) directions prevail. The highest dust content of the atmosphere is in the northwestern and western regions of Karakalpakstan, the lowest in the southern regions (Fig.5).

Figure 5. Dust concentration in the regions of Karakalpakstan

Depending on the wind speed, from April to October, the dust content of the atmosphere of the northwestern part of Karakalpakstan increases on average from 48.5 to 106.8 µg/m³, the dust content of the atmosphere of the southern part of Karakalpakstan increases from 13.2 to 33.4 µg/m³ with an average monthly dust MPC of 100 µg/m³ (Hygienic standards, SanPiN RUz, No. 0293-11). The largest contribution, as can be seen in Fig.4, is made by Ustyurt with a more active wind regime. Then, descending, salt dust flows from Aralkum, dust sand flows from Kyzylkum and Karakum. The smallest contribution to the dustiness of the Karakum atmosphere is explained by the fact that southerly winds are relatively rare in the Southern Urals (4%).

Conclusion. The dustiness of the atmosphere of the Lower Amudarya oasis, where the majority of the population of Karakalpakstan, the entire population of Khorezm and the Tashauz region of Turkmenistan live, determines the relevance of research aimed at quantifying the spatial and temporal dynamics of dust concentrations, the sources of which are the vast desert territories surrounding the oasis. Model calculations from April to October 2023 showed that Ustyurt and Aralkum make the greatest contribution to the dustiness of the atmosphere of the Lower Amudarya oasis. The dust content of the atmosphere of the Lower Amudarya oasis in April, May, July, August and September exceeds the average monthly dust MPC.

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