Candidate of Chemical Sciences, former employee of the Department of Meteorology and Climatology, Faculty of Geography, Lomonosov Moscow State University. Lomonosov Irina Eremina said that dirty rains fall in Moscow mainly after a long drought.
At the same time, the expert noted that such rains do not account for more than 3% of precipitation. According to her, rainwater is the purest water on Earth, especially if it rains often and abundantly. For example, if a monthly rain falls, it will be the purest rain. And if there was no rain for a long time, and then it was not strong, then this will be the dirtiest rain.
As an example, Eremina recalled July 2010, when there was smog and no rain. The rains that followed were very dirty. Such precipitates differ from ordinary ones both in the concentration of substances and in their composition.
The chemist explained that, like any natural water, rain has approximately the same composition. Contains cations (calcium, sodium, potassium, magnesium, ammonium), anions (sulfates, chlorides, nitrates, bicarbonates). “Among the anions are both fluorides and phosphates, but in very small amounts. And not in all the rains they are, only in the dirty ones.