ИСТИНА

Chemical composition of atmospheric precipitation in the region of Moscow State University was analyzed on the basis of environment monitoring of every event of wet-only sample during the period from 1982 up to now. Every year we have got about 100-150 probes of rain and snow. Concentrations of sulfate (SO42-), hydrocarbonate (НСО3-), cloride (Cl-), nitrate (NO3-),: calcium (Са2+), magnesium (Mg2+), sodium (Na+), potassium (K+) and ammonium (NH4+) as well as pH and specific conductivity were measured. The analysis of the chemical composition of precipitation and its acidity carried out at the Meteorological observatory of Moscow State University demonstrates significant seasonal and interannual variability. The entire more than 30-year period of observations can be divided into 3 parts with different acidity, changing mineralization and different predominant ions. The percentage of acid precipitation with pH < 5 is about 21 % for a year on average. There were no practically samples of acid rain in 1999 – 2004. Before 1999 and the last years we have 25-30% probes of acid rains every year. The volume weighted mean long-term рН is 4.9, and mean value of precipitation mineralization is 17.5 mg/L. Average annual values of precipitation mineralization varied from 11.8 mg/L (2001) to 27.0 mg/L (1991). Mean mineralization was about 20 mg/L till the late 1990s and about 15 mg/l in recent years. At the beginning of our observations (in 80-90s) sulfate-ion was predominant in precipitation samples. The content of hydrocarbonate ions increased during the period of the absence of acid precipitation (1999–2004), and the concentration of chlorides started increasing considerably since 2005. In seasonal variations majority of ions and mineralization have max concentrations in spring. Under investigation of seasonal snow pack samples we have found that samples of snow pack gathered in the center of Moscow were 3 times more contaminated than in the sub Moscow area samples and 5 times more dirty than snow pack probes in meteorological observatory of the Moscow State University.