## 4 Discussion
Surprisingly, the results obtained in 2015-2020 demonstrate no statistically significant intra-annual variations in the concentration of inorganic nitrogen in atmospheric depositions in both locations in this period (Figures 2 and 3). To make the situation even more complicated, there was observed a slightly (but statistically insignificant) increase in concentrations of inorganic nitrogen in Katsiveli in the warm period of year (Figure 3b). There are several possible reasons of these dramatic changes in seasonal variations of inorganic nitrogen volume-weighted mean concentrations. They can result from significant changes in the volume of anthropogenic emissions to the atmosphere as compared to the period before 2014, that is, an increase in the quantity of marine, aviation and other  
Figure 5: Intra-annual variations of the inorganic nitrogen volume-weighted mean concentrations in the atmospheric depositions in Sevastopol (**a**) and Katsiveli (**b**) in 2007–2008. transportation in Crimea, especially in summer. For example, the number of auto-vehicles in Sevastopol increased twofold from 2015 to 2017. The number of large city boiler houses in Sevastopol increased from 116 in 2014 to 133 in 2016, but these boilers utilized natural gas instead of coal. This suggests qualitative and quantitative changes in local anthropogenic sources of inorganic nitrogen to atmospheric depositions. Intra-annual variations of volume-weighted mean concentrations (excluding cases of extremely high concentrations) of inorganic phosphorus reveal no statistically significant variations (Figure 2c,d) in Sevastopol, while these values increase in Katsiveli in April-August (Figure 3c,d). Considering that phosphorus is mostly of lithogenic origin in the atmosphere, this difference between Sevastopol and Katsiveli is due to different sources of dust in the air. Anthropogenic activities, transportation, and excavations are intensive in Sevastopol in all seasons providing an even background level of the phosphorus input to the air and on average 0.42 uM of inorganic phosphorus in atmospheric depositions. Anthropogenic activities in Katsiveli are far less intensive, as compared to Sevastopol, and a background concentration of phosphorus in the atmospheric depositions for low-seasons is about 0.2 uM, but it increases in the high-season due to the several-fold multiplying population and anthropogenic activities in summer. Additionally, a dramatic decrease of precipitation events in summer period and windy weather conditions support an additional source of soil dust to the air and dry atmospheric depositions. The concentration of silicon in atmospheric depositions dramatically increases in Katsiveli on summertime (Figure 3f). This behavior of silicon is similar to phosphorus. We assume that the reasons for this intra-annual variations in the concentration of silicon are also similar to those for phosphorus. Silicon is a lithogenic element and a dramatic decrease in rain precipitation in Crimea in summertime and additional input of silicon to the atmosphere in dry windy conditions result in the observed high concentrations of this element in atmospheric depositions even though extreme events of long-distance transport of dust from the Sahara and Syria deserts are excluded. If high summertime concentrations of silicon are excluded, the average concentration of silicon in the area of Katsiveli is as low as 0.3 uM, which is typical for natural coastal conditions. The average concentration of silicon in atmospheric depositions in Sevastopol is several-fold of that value in Katsiveli (Figures 2 and 3). Similar to phosphorus, this demonstrates the presence of powerful local anthropogenic sources of this element to the air and then to the atmospheric depositions. The Redfield ratio is often used to assess the effect of nutrients (inorganic nitrogen, phosphorus) input with atmospheric depositions on primary production [11; 30; 31; 32].