ИСТИНА

Air is one of the most important resources for the maintenance of human life with a complex gas composition. But also it contains many different suspended or blown by the wind particles, whose influence on people and nature cannot be neglected. Such particles can have different genesis, vary in size, shape, chemical composition and other parameters. Particle transport is the process of particles movement in a medium (in air) under the influence of external forces. First of all, it is determined by the flow characteristics, location of sources, the presence and placement of obstacles (buildings, trees, etc.) and deposition surfaces. Partially, the transfer is determined by the properties of each individual particle: radius and density. In an area that has not experienced human impact, the phenomenon of particle transport rarely poses a serious danger to humans or the ecosystem. For natural particles, allergy, desertification, soil depletion can be mentioned as common examples of negative effects. The urban environment cannot function without transport and anthropogenic structures - sources of technogenic emissions, including various solid and liquid particles that get into the air and often have a stronger (comparing to natural particles) negative impact on human, animal and plant health. Spatial heterogeneity of emission sources and the complex geometry of urban development greatly complicate the process of particle transport, so it can lead to high concentrations and accumulation of particles in limited areas [2]. In the urban environment, anthropogenic and natural components are present, and therefore the transport also changes for natural particles: plant pollen, snow, water drops, dust, and others [1]. Burning of various substances and the release of harmful combustion products into the atmosphere are usual for industrial areas and landfills. There are also weather conditions characterized by high wind speeds - in such situations, the level of emission of rare and heavy particles, such as sand, soil particles and road dust, can significantly increase. To account for such cases, it is necessary to conduct special studies. Thus, the direct influence of the transfer of particles in an urban environment on human health and the environment determines the great importance of the problem of modeling and forecasting this phenomenon. In recent years, with the development of technology, more and more powerful computational capabilities and hydrodynamic models with high spatial and temporal resolution have become available. First of all, the efforts of the developers of such models are aimed at increasing the accuracy of forecasting the basic meteorological parameters at the macro and mesoscale. Particle transport receives less attention, since usually the accuracy of simple modules and parametrizations is sufficient for researchers, especially at the mesoscale. However, even the available microscale models of particle transport do not allow describing the specificity of the transfer in the atmosphere of the entire diversity of particles of different shapes, sizes and masses, since only some of the parameters can be set. It limits the possibilities for studying the transport and sedimentation of particles. Also, integrated in complex microclimatic or meteorological models modules for transferring various pollutants are tied to a specific product and, accordingly, inherit possible limitations and errors of its methodology. In this paper, a multipurpose computational algorithm is created to describe the maximum diversity of particles under different meteorological conditions and different building geometry. At this stage, the finished result is a technology that allows to evaluate the distribution and sedimentation of spherical particles of various sizes and masses on the scales of tens and first hundreds of meters, taking into account the predetermined geometry of buildings and fields of meteorological quantities. The algorithm also allows the use of various methods of accounting for turbulent motions, resistance forces and other factors affecting the process of particle transport. In this model, the particles interact with the quasi-stationary flow given by the initial data. The motion of particles is described by Newton's second law, differential equations are being solved by the fourth order Runge – Kutta method. Subgrid turbulence is parametrized by the discrete random walk model. The difference from the majority of such embedded tools is the ability to use initial data from different sources, for example, different hydrodynamic models. It allows both to choose the most accurate and representative model for a particular case and to compare the results with the data of particle transfer modules, which are built into these models, and even verify technology. During the development period, the microscale threedimensional non-hydrostatic model ENVI_MET version 4.4 (update of November 2018) was used to obtain the initial meteorological data: wind speed and direction, turbulent kinetic energy values, dissipation and other parameters. This solution can be used both for scientific and practical purposes for specific situations. At present, both a series of test cases are modeled to study the effect of various modules of the model on the result, as well as a complex of situations close to real conditions and buildings. In future work, it is planned to add methods of interaction with more complex particle forms, for example, to study the transfer of suspended water and ice particles.