## 1 Introduction
### Brief Introduction to Pollutant Dispersion  
The gaseous envelope surrounding the Earth, as well as other planets in the Solar System, is called the atmosphere. The gases contained in the Earth's atmosphere create atmospheric air. Its permanent components are [1]:  
* molecular nitrogen \(N_{2}\) in excess of 78%;
* oxygen \(O_{2}\), slightly less than 21%;
* argon \(Ar\), 0,9%;
* neon \(Ne\), helium \(He\), krypton \(Kr\), xenon \(Xe\);
* hydrogen \(H_{2}\), ozone \(O_{3}\) in trace quantities.  
The emission of atmospheric air pollution takes place in the lowest layer of the atmosphere--the troposphere [1]. This dependence is crucial because the mechanisms that allow the dispersion are taking place in this particular layer.  
The composition of the atmosphere is strictly defined, and any exceeding of the set standard becomes pollution. The pollutants that are emitted into the atmosphere have a destructive impact on human health as well as on the environment [2,3]. However, this occurs not only in the immediate vicinity of emission sources, as the observed effects are global in nature [4]. Any emission is always connected with the process of propagation caused by the circulation of air masses, which is influenced by many factors correlated with the characteristics of the land [5] as well as with meteorological conditions [6,7]. In view of the harmful effects on human health, the most dangerous group are dust particles (named Particulate Matter, PM, in the literature), which, due to their particle size, penetrate deep into the lungs and then are able, like oxygen, to enter the circulatory system. Depending on the particle size, differentiation is made between [8]:  
* PM 10--particulate matter fractions of aerodynamic diameter in the range: (2.5 \(\upmu\)m; 10 \(\upmu\)m);
* PM 2.5--particulate matter fractions up to 2.5 \(\upmu\)m in diameter;
* TSP--total suspended particulate matter.  
Places from which harmful substances are released into the atmosphere are referred to as sources of pollution:  
* Natural sources, related to the functioning of nature;
* Man-made sources, related to human activity.  
Man-made sources of pollutant emission can be divided into [9,10]:  
* Point sources--the release of pollutants into the atmosphere takes place in a volume much smaller than the considered pollutant transport distance (chimneys [11], ventilation shafts, households);
* Linear sources--the release of pollutants into the atmosphere takes place along a straight line or curve of a length comparable to the considered pollutant transport distance (roads [12], motorways, open sewage channels). For the purposes of calculation, such an emission may be treated as a set of point sources;
* Surface sources--the release of pollutants into the atmosphere takes place from a plane, and the dimensions of the plane are comparable to the considered pollutant transport distance (re-emission of pollutants from waters [13], sedimentation tanks, waste dumps);
* Volumetric sources--the release of pollutants into the atmosphere takes place in a volume of dimensions comparable to the considered transport distance (e.g., volcanic emission [14] including emission from lava and ash clouds).  
The process of dispersion of pollutants in atmospheric air is characterised by a description containing complex parameters, which are variable both in time and space [15]. To deal with this class of issues, a number of mathematical and physical models have been developed and are now being applied for decisions related to improving air quality in the light of the developing infrastructure [16].