In Moscow, rain is rarely classified as heavy pollution, and studies suggest that dark or dirty showers make up only a small fraction of total precipitation, often occurring after extended dry spells. Expert commentary from a chemical scientist who previously worked at the Department of Meteorology and Climatology within the Faculty of Geography at Moscow State University has been shared to shed light on this topic. The insights come from a specialist associated with Socialbites, who is recognized for examining how atmospheric processes influence water quality.
According to the specialist, rainwater itself is largely composed of pure water, particularly when rainfall is frequent and intense. There are moments when a forecast promises rain for an extended period, and during such times the rainfall can carry fewer impurities. Conversely, after a long dry interval followed by a heavy downpour, the rain may appear dirtier because the atmosphere has accumulated more substances that get washed out of the air by precipitation. This phenomenon has practical implications for water quality over short timescales and helps explain why not all rain seems equally clean.
In recounting a notable example from 2010, the chemist notes that a July with smoke and without rain was followed by rain that appeared unusually dirty. The change in air conditions, including lingering pollutants, can lead to rainfall with higher concentrations of particulates and dissolved substances. Such rain differs from typical precipitation not only in the amount of material it carries but also in the specific chemical makeup of those substances.
The chemist explains that natural water, including rain, shares a broad chemical profile. The common constituents include cations such as calcium, sodium, potassium, magnesium, and ammonium, along with anions like sulfates, chlorides, nitrates, and bicarbonates. Very small amounts of fluoride and phosphate can also be present. Importantly, these latter components are not necessarily found in every rain event, but may appear more prominently in rain that has passed through more polluted air. This description helps clarify why rainwater can vary in quality from one occurrence to the next.
In addressing public questions about rainwater safety, the expert has discussed whether consuming rainwater is advisable. The explicit takeaway is that while rainwater could be clean enough to drink under certain atmospheric conditions, its safety depends on the purity of the air at the time of rainfall and the presence of any contaminants or particulates that may have been collected along the way. Historical examples highlight that even natural water sources require consideration of local air quality and environmental conditions before evaluating suitability for drinking.