The study of the aerodynamic characteristics of dust particles in the air of roadside areas

The article addresses issues, which are related to the determination of aerodynamic characteristics of dust particles in roadside air areas. Was studied dustiness of Volgograd roadside areas.


Introduction
Dust particles, produced by road traffic, considered as an important source of air pollution, since the vehicle fleet is increasing worldwide, therefore, increasing exhaust emissions, as well as particles from tire abrasion and road wear coverings. Emissions without exhaust gases will be important in the future as well, even if the vehicle fleet will be fully electrified [1]. With the exception of emissions directly into the air, particles settle and accumulate together with dust from other sources on road surfaces, forming road dust. Dust is delayed by traffic and / or wind and contributes to air pollution. Sources of road dust strongly differ geographically and in time. Conventional sources are particles of brake and tire wear. Particles of road dust are in a turbulent flow and have aerodynamic diameter from a few nanometers to tens of µm ( Fig. 1) [2,3]. The settling process of small weighted particles by gravity in a turbulent flow is composed from two processes: a) continuous subsidence of some parts down, inside carrying them pulsating moles, and b) random in direction, frequency and amplitude of particles movement with descents and rises along with carrying them pulsating moles [4]. The sedimentation speed of spherical particles was studied theoretically and experimentally in a wide range of Reynolds numbers. For spherical particles, when calculating the sedimentation speed, there are either theoretical formulas or semi-empirical ratios that describes the experimental data.
[5] There are no theoretical models for calculating the sedimentation speed of particles with complex geometric shape (for example, particles of anthropogenic natural dust, dust storms, pollen of plants, powder materials), and therefore, exist several experimental methods.
The first settling process of small suspended particles by gravity in a turbulent flowcontinuous settling of particles down, despite the pulsating movement of carrier gas moles, is described in the Stokes approximation by the equation, Where g -acceleration of gravity; -particle relaxation time. This expression is derived for the case of free sedimentation of particles in a stationary laminar flow. The equation of the vertical motion of a Stokes particle in a horizontal flow by gravity, has the form: -settlement speed of particle; t --particle -Langrangian ripple frequency; V'amplitude of the transversal component of the speed pulsation of turbulent flow.
It should also be emphasized, that the shape of the particle has a major impact on the aerodynamic properties and on the trajectory of the dust particles movement.
The complexity to determine the sedimentation speed of road dust is also to the fact, that there is a problem in selection of these dust particles.
The authors [6] suggested a method to determine equivalent aerodynamic diameter of aerosol particles with non-spherical shape, when they settle in the field of gravity in the range of Reynolds numbers from 0,1 to 6,0.
Particles, if they are not too large, react to random turbulent pulsations of the environment and along with translational motion, together with the flow, they make, under their influence, a pulsation (oscillatory movement) relative to carrying them gas moles and random movement along with the moles of gas, called turbulent diffusion of particles.

Methods
Like the motion of gas moles, the pulsating and diffusive particle movement are random (stochastic) in nature and therefore described statistically. The settling of particles by gravity has the same nature: the particles settle down, making random descents and ascents together with the pulsating moles, carrying them. [4] The special theory of stationary random processes, or, more precisely, the theory of stationary, received the good interest in practice. Random functions (since the argument of a stationary random function in general case, may not be time).
For a stationary random [7]: -mathematical expe -mathematical expectations of sections, relevant to the fixed values of the arguments t1 and t2.
The ordinate distribution density of a random function f(C|t) and the speed distribution Denote these densities correspondingly f(C) and f(C, V). Then the average residence time of the stationary random function is higher than given level C time and the average output duration is determined by formulas (4-6).
This method allows to obtain the characteristics of the dispersed dust composition in the air, and to determine the average residence time of the fractional concentration above given level, i.e. to predict the content of small-dispersed dust, depending on various conditions, and to assess the impact on people's health, that live near highways.

Results and Discussion
Also, the authors of the article conducted studies on the roadside territories of the urban environment of Volgograd. The importance of the urban pollution by small-dispersed particles was highlighted in works [8][9][10][11]. For the study, 50 measurement points were selected at various intersections of the city. For measuring was used a manual particle counter HANDHELD 3016 IAQ (made in the USA). The manual particle counter HANDHELD 3016 IAQ is used to measure the mass concentration of aerosol particles of different fractions (PM0.5, PM1, PM2.5, PM5, PM10, TPM, where PM0.5 is the concentration o