— Irina Dmitrievna, you have been studying the composition of the Moscow rains for 40 years in a row. What substances do they contain?
– Any natural water, including rain, has approximately the same composition. Components are the most common. Cations – calcium, sodium, potassium, magnesium, ammonium. Anions – sulfates, chlorides, nitrates, bicarbonates. Anions include both fluorides and phosphates, but in very small amounts. And not every rain – only dirty ones.
But in general, rain is the purest water in the world. Especially if they get frequent and heavy rainfall. When they say, “It will rain for a month,” it is the purest of rains. There will be all the same components determined in all waters, but present in very small amounts, at the sensitivity limit of the assays. No wonder they collected the rainwater for drinking because the rain was soft, so there was very little salt there.
– And in dirty rain, the same components are found in large quantities?
– Yes. If it does not rain for a long time, then it rains and is not yet heavy, this will be the dirtiest rain. Remember 2010, July when the fog stopped and it didn’t rain? And then they fell by 0.5mm, by 0.6mm? They were very dirty here.
How much dirty rain does it usually rain in a year?
– If the mineralization of all components (anions plus cations) is more than 100 mg / l, it is a dirty rain. Sometimes there are five or six such rains per year, and sometimes one or none, and on average this value does not exceed 3%. The average mineralization of the sediments during 40 years of observation at the meteorological observatory of Moscow State University was 17 mg/l.
— Are there acceptable limits for the content of the various components in the sediments?
– There are no rules for rain. For drinking water, if there are standards for maximum allowable concentrations (MPC) for air, then there is no MPC for rain. Because in any tap water you will find the same sulfates, chlorides, nitrates, calcium, magnesium, but in more than the average rainfall.
– But still there are nitrates in the rain?
— Yes, from emissions from businesses and vehicles. There are many reactions with water droplets in the air. They can be found everywhere, including nitrates.
— Did you also examine the snow samples?
– Yes, once a year I collected seasonal snow samples in the Leninsky district, and then in other parts of Moscow. Seasonal snow is a sample of all snow thickness for the winter before the snow melts. With the help of a snow tube, I took a snow sample for the entire height of the snow cover – everything that attacked from November to March.
I tried not to take the paths with snow accumulations from the sidewalks to the edges, and to take a sample from the park where the snow was untouched.
– In one of your posts it says that snow is cleaner in the north of Moscow, and the dirtiest in the south. Is it exactly the same now?
“It really was then. But while we believe we get clean precipitation from the Arctic Ocean, these are not always global consequences. For a large city like Moscow, the impact of pollution sources close to the sampling site will be greater.
— How far from an industrial establishment do you have to live for it to rain in your area?
– Depends on the wind rose. Where the wind blows more often, the pollution will be carried there and it will be cleaner on the leeward side. We should also not forget about the speed of chemical reactions. The plant that was thrown an hour ago does not have to be here and now, it will fall. There is a mixture of air mass. The rain did not fall immediately and swallowed everything. Rain already contains substances that will react with substances entering the droplet path, compounds are formed there and the dirt from the factory can be blown away.
Here, it is not possible to say that it is always clean from the north and dirty from the south. Multi-factor.
– Acid rain scared everyone in Soviet times, they said that all people can go bald …
– Yes. And that the raincoats will be in the holes …
What is acid rain and is it really dangerous?
– The concentration of hydrogen ions, which are responsible for both the mineralization, that is, the content of basic ions and the acidity of precipitation, are observed in a wide range in nature.
The pH index is the concentration in the converted, human-readable form of the hydrogen ion.
pH7 is the neutral point. The range of change is from 1 to 14 pH, the number 7 is in the middle. Anything less than seven is considered acidic, anything more than seven is considered alkaline. The pH of tap water is close to neutral.
As for the atmosphere, rains, snowfalls, collected in the cleanest area, away from all pollution sources, highways, will never be 7, close to 5.6 because there is carbon dioxide in the atmosphere, and then it dissolves in moisture droplets to form weak carbonic acid.
– It turns out that we always have acid rain?
– NO. When I started working in the 80s, the World Meteorological Organization decided to study the same acid rains. They created five reference points where there was an absolutely pure atmosphere – for example, I remember the island of Amsterdam in the middle of the Indian Ocean. So even at these points the precipitation was below pH 5.0, not 5.6.
And since the 80s of the last century, they began to take into account not only carbon dioxide in the atmosphere, but also other natural acid-forming factors, therefore, those with a pH of less than 5.0 are considered acid rain. And we call rains between 5.0 and 7.0 pH balance and neutral. And only after 7 it is already alkaline. In my 40 years of observation, my most acid rain fell in July 1987 with a pH of 3.2, and the most alkaline rain fell in November 1983 – 9.65 pH.
– How much rain does it rain in three to one year?
– I think not more than five per year, on average 1.8%. This was the case from 1980 to 1998. But from 1999 to 2004, there was no acid rain. It seems that during these years the industry in Moscow was idle. Surprised, I double checked all my devices. Summer is coming and the acid rain is gone again. They reappeared in 2005, however, and continue to decline to the present day.
Do acid rains usually occur in summer?
– Yes. And the peak is usually in July. While summer precipitation creates the lowest average pH values, it is close to the sixth average in winter. Usually during the summer months, even from May to September, the average pH is below five, meaning the average pH for the month is acidic.
– Is it temperature dependent?
“It depends on everything: temperature, pollution, humidity and emissions. Scientists can’t name the exact cause yet.
— Could the dreaded acid rain and alkaline rain be harmful?
– Everything is relative. If you measure the acidity of juice or wine, the pH will be lower than that of rain. The pH of wine is about 3.5. But if you pour wine on your head, no one will go bald. Also, acid rains do not fall very often.
– Are alkaline rains with a pH of 9.0 less common than acid rains?
“I have experienced something like this once in forty years. This is 1983 – the very beginning of my research. And it is not clear what it is connected with. Even pH 8 for precipitation is observed very rarely, 0 to 3 cases per year and more often 0.
Can you drink rainwater now like our grandmothers used to do?
— No, I would not recommend it, especially in Moscow. There are too many emissions, too many vehicles. It can be a lot of dust, soot, emissions and finally bacteria. Toxic metals may also be contained, albeit in micrograms, but their harm can be significant. As a matter of fact, rain water is generally the cleanest of natural waters, but this does not mean that it is drinkable.