## 4 Discussion  
The formation of the chemical composition of precipitation depends on various factors, first of all, the content of various substances in the atmospheric air. The input of nutrients into the atmosphere can be natural or/and anthropogenic. The presence of nitrogen in the air is often associated with anthropogenic sources. Industrial production of nitric acid, fuel burning, motor vehicle exhaust gas and further development of transport are the main sources of nitrogen oxide emissions. About 90% of ammonium emissions come from agriculture and industrial ammonia production [23]. The main natural sources of phosphorus in the atmosphere are wind erosion of soil in areas with arid climates; generation of biogenic aerosols by terrestrial vegetation (spores, pollen, plant residues, etc. ); destruction of sea spray on the surface of reservoirs, as well as volcanic activity. Anthropogenic phosphorus input is associated with the production and utilization of fertilizers, as well as with metallurgical industries [5]. Silicon in the atmosphere is associated with airborne particles from industrial areas or transported with dust from deserts. Global dust emissions range  
Figure 4: Variations of inorganic phosphorus (**a**,**b**) and silicon (**c**,**d**) concentrations in the atmospheric depositions in Katsiveli (**a**,**c**) and Sevastopol (**b**,**d**). Red line—volume-weighted mean concentration of nutrients, orange ovals—cases of significant excess of inorganic phosphorus and silicon concentrations. from 1000 to 3000 Mt/yr [24]. Then all these nutrients are transported from the atmosphere to the underlying surface with atmospheric depositions. Many researchers [25; 26; 27] argued that dry depositions contribute equal or greater amounts of nutrients, as compared to wet depositions. When it comes to silicon, it is in the form of lithogenic silica and silicates and it is transported with airborne particles, originated from industrial burning and/or soil particles [28]. Thus, the content of silicon in samples from open samplers for wet and dry precipitations may dramatically exceed the content of silicon in samples from wet-only samplers. A similar situation is for phosphorus in the form of phosphate [25; 27; 29]. The average contribution of dry depositions is about 208% for phosphorus, while it is about 405% for silicon. These values agree with data [30], where the concentration of inorganic phosphorus in dry depositions are on average 2.8-times higher than that in wet precipitations. Yet, nitrogen is usually in the form of dissolved and gaseous compounds, thus contribution of dry deposition of nitrogen is less important, as compared to silicon and phosphorus. Indeed, the average contribution of dry depositions for inorganic nitrogen is about 22-26% at Sevastopol (Table 1) and 17-21% at Katsiveli (Table 2) in 2015-2020. Our results on nitrogen deposition are in line with the results [29], which have assessed contributions of wet and dry depositions to the total amount of NOx are similar. In previous studies [15], we have demonstrated that the monthly volume weighted mean concentrations of inorganic nitrogen in atmospheric depositions in Sevastopol (the urban site) increase in the cold season (Figure 5a). We have assumed that this increase is a result of burning fuel (gas, coal, oil) to produce heat in October-March. Furthermore, there is a clear difference between intra-annual variations of nitrogen concentration in Sevastopol and Katsiveli. These oscillations of the monthly volume weighted mean concentrations in rural site are statistically insignificant (Figure 5b). We have explained this fact by the absence of powerful local sources of air pollution (neither agricultural, nor industrial) in Katsiveli. Thus, the situation with powerful local sourced and seasonal variations in inorganic nitrogen in Sevastopol has been recognized as clear and reasonable.