Variability in Acidity of Precipitation on the Territory of the Far Eastern Federal District of Russia.

An analysis is made of the variability of the acidity index of precipitation and fluxes of wet sulfur and nitrogen deposition on the territory of the Far Eastern Federal District of the Russian Federation (FEFD). The analysis uses data of Roshydromet (Hydrometeorological Service of Russia). It is found that alkaline precipitation is characteristic for most of the FEFD (Yakutia and Transbaikalia). However, an increase in the acidity of precipitation is observed in the southeast of the region during the period under consideration. The average annual pH values of precipitation in Primorskii krai dropped below 5.6 in the first decade of the 21st century to reach 4.6–4.7 in particular years at some of the monitoring stations. It is pointed out that the ever-increasing use of nitrogen fertilizers in East Asian countries leads to an increase in the flux of atmospheric nitrogen deposition, which negatively affects forest vegetation. The annual flux of wet deposition at the EANET Primorskaya international monitoring station between 2006 and 2015 was 6.37 kg/ha per year for S deposition and 6.3 kg/ha per year for N (nitrate + ammonium). Similar values were obtained by averaging data from all stations in Primorskii krai. In 2018, this flux exceeded a critical value of 10 kg/ha per year. The Ternei monitoring station located in the Sikhote-Alin Biosphere Reserve observed twice as few nitrogen fluxes as that at the Primorskaya station, but an order of magnitude higher than the values recorded in the western part of FEFD. The determining factor for an increase in the acidity of precipitation and for the high levels of nitrogen depositions in the south-east of FEFD is the transboundary atmospheric transport of pollutants from the centers of anthropogenic emissions in East Asia. The analysis of data made in this paper is in agreement with reports of Roshydromet on the state and pollution of the environment of the Russian Federation and supplements and details them. [ABSTRACT FROM AUTHOR]