## 1 Introduction
These in turn allows to take specific actions aimed at reducing air pollution with solid particles [28; 29]. The chemical composition of fine PM (PM\({}_{2.5}\)) differs significantly from the coarse PM fraction (PM\({}_{2.5-10}\)), which is mainly due to their different origin and life time [2; 14; 30]. Numerous studies indicate that the main constituent of fine and ultrafine particles are, in particular, carbonaceous aerosol and water-soluble inorganic ions, for example, [31; 32; 33]. The contribution of sea spray and crustal dust in PM\({}_{2.5}\) and PM\({}_{1}\) mass is much lower compared to coarse PM. However, in specific locations, it can be quite significant [19; 28; 34]. In the urban air, particularly in areas with high population density, carbonaceous aerosol can reach very high concentrations [35]. Literature data report that, in urbanized areas, carbon particles can account 40-50% of fine PM mass [3]. Other studies indicate that the share of elemental and organic carbon in PM\({}_{2.5}\) from sites located in moderate latitudes varies between 5-9% and 20-50%, respectively [36]. Carbonaceous matter bounded with atmospheric aerosol, named total carbon (TC), consist of elemental carbon (EC), inorganic carbon (IC, or carbonated carbon--CC) and organic carbon (OC) [2; 3]. However, most commonly used analytical methods allow for determination of EC and OC contents in aerosol particles. Elementary carbon is emitted to the atmosphere mostly as primary pollutant, mainly as a result of incomplete combustion of fossil fuels and pyrolysis of biological material during combustion [32; 37]. In turn, organic carbon can come from both primary (primary organic carbon, POC) and secondary sources (secondary organic carbon, SOC). The latter are related to oxidation of precursors such as volatile organic compounds of biogenic and/or anthropogenic origin [32; 38; 39]. Secondary organic aerosol (SOA), formed as a result of VOC oxidation, is an important part of the PM mass, especially during the summer in areas covered with vegetation [31; 40]. According to the 2013 EEA report [41],organic substances constitute on average about 30% of the PM\({}_{2.5}\) concentration and about 20% of the PM\({}_{10}\) concentration, measured at regional background stations in Europe. Water-soluble ions, next to elemental carbon and organic matter, constitute an important part of fine particulate matter. PM-bound inorganic ions were intensively investigated and many studies showed that they have a significant influence on natural environment. These compounds can alter the chemical properties of other particles [1; 42], they have also ability to scatter light and therefore modify visibility. They can also act as cloud condensation nuclei and thereby directly or indirectly affects the climate [3; 43]. Moreover, they are among the most common substances contributing to the atmospheric acidity [44; 45]. Numerous studies indicate that water-soluble ions in suspended particles play a significant role in atmospheric chemical reactions acting as precursors for new particles, especially sulphates (SO\({}_{4}\)[2]-), nitrates (NO\({}_{3}\)[3] and ammonium (NH\({}_{4}\)[46; 47]. Secondary Inorganic Aerosol (SIA) is produced in the atmosphere through (photo-)chemical reactions of gaseous precursors (such as NO\({}_{x}\), SO\({}_{2}\), or NH\({}_{3}\)) that may react with O\({}_{3}\) and other reactive molecules (including radicals) to form mainly ammonium nitrate (NH\({}_{4}\)NO\({}_{3}\)), ammonium sulphate ((NH\({}_{4}\))\({}_{2}\)SO\({}_{4}\)) and ammonium bisulphate (NH\({}_{4}\)HSO\({}_{4}\)) [32]. In the atmosphere poor in ammonia, nitrate and sulphate can easily react with the sea salt and crustal aerosols. It results in the formation of calcium and sodium sulphate (respectively: CaSO\({}_{4}\) and Na\({}_{2}\)SO\({}_{4}\)), as well as calcium and sodium nitrate (respectively: Ca(NO\({}_{3}\))\({}_{2}\) and NaNO\({}_{3}\)) in the coarse particles [3; 9].