HORROR IN A RAINDROP: the «eternal substance» attacking our planet

Photo by freddie marriage on Unsplash

What interesting things can be found in a drop of rain? Recent scientific studies reveal quite a lot. A raindrop is a miniature chemical reactor, and the processes taking place inside it affect human health and, more broadly, life on our planet.

THE ERA OF ACID RAIN

he acidic reaction of rainwater was discovered in 1696 by Anglo-Irish chemist and theologian Robert Boyle. However, he did not understand what was happening or why the water turned cloudy. The mystery was solved in 1852 by an amateur photographer from Manchester, who, for some reason, added a barium salt solution to rainwater. By observing the reaction, he realized he had found sulfuric acid in the rain. Naturally, the scientific community mocked him at first — after all, science at the time believed that carbon dioxide in the atmosphere simply dissolved in water droplets, forming a weak carbonic acid.

And who was this photographer, after all, to claim a scientific discovery? But later, his findings were confirmed, and researchers found not only sulfuric acid in rainwater, but also nitric, formic, oxalic, and acetic acids. It wasn’t difficult to do — the Industrial and Technological Revolution of the 19th century was in full swing. The massive burning of fossil fuels released vast amounts of carbon and sulfur dioxide into the atmosphere. Thus began the era of acid rain.

THE TERRIFYING SECRET OF TILED ROOFS

At first, scientists viewed acid rain quite favorably. If rain brings sulfur and nitrogen to the fields, isn’t that a wonderful fertilizer? But soon the optimism faded. It turned out that acid rain acidifies soil, killing the biota within it and drastically reducing crop yields. Moreover, it weakens the immune systems of trees, leading to forest die-offs, and completely wipes out all living organisms in enclosed bodies of water. The rise in cardiovascular and respiratory diseases is also their doing.

The Industrial Revolution destroyed millions of lives, thousands of hectares of forest, and countless beautiful lakes across the United States, Canada, and other countries. It also changed the face of cities. The yellowish tint of the Taj Mahal and the green color of the copper Statue of Liberty are both legacies of acid rain. In 2009, acid rain eroded the base of a mountain in China’s Wulong County, triggering a landslide that claimed 74 lives. The beautiful tiled roofs that appeared on European houses did not emerge from prosperity — acid rain easily corroded metal and stone, while tiles could withstand it much longer.

HOW CLOUDS TRAVEL

In 1972, the UN recognized acid rain as an environmental problem of international scale. Since then, the ecological situation in Europe and America has greatly improved, yet a raindrop remains a raindrop — a substance of extremely complex chemical composition. In addition to acids, it contains ions of ammonium, iron, sodium, calcium, manganese, and magnesium. All this hovers above the Earth as a cloud until it falls as rain. Roughly half of our planet’s sky is constantly covered with clouds, which mostly drift within the troposphere, at altitudes ranging from 1 to 5 kilometers above the ground.

Over time, a cloud dissipates completely, except for about 15% of its mass, which falls to Earth as precipitation. Depending on the humidity and temperature where this happens, it may reach the ground or evaporate on the way. A single cloud lives for about an hour, but by evaporating and condensing again, it can travel for many kilometers. This phenomenon even has a special term — «transboundary transport». Because of it, an acid cloud can form somewhere in the United States and then fall as acid rain over Canada.

HOW DROPS ARE BORN

For water to turn into a droplet, it needs a condensation nucleus. Over seas and oceans, salt crystals serve this role. But when clouds form over industrial areas, any other particles can act as such nuclei — for example, iron and manganese oxides emitted by factories. As a result, each droplet becomes a kind of chemical reactor, producing an entire set of acids. In marine clouds, their concentration is negligible. But over industrial zones, where SO₂ levels are much higher, reactions proceed differently — and the formation of sulfuric acid follows a much more dangerous scenario.

To be fair, acid rain can be triggered not only by human activity — sometimes natural phenomena are to blame. In 2014, for instance, Iceland’s Bárðarbunga volcano released more than 11 million tons of SO₂ into the atmosphere over six months of activity. However, humanity has long outdone the volcanoes: in 2019, the amount of sulfur dioxide emitted by the South African energy corporation Eskom exceeded that of entire national energy sectors, including those of the United States and China.

SCRUBBERS — EFFECTIVE BUT EXPENSIVE

At some point, it became clear that to avoid completely destroying the environment — and along with it, human health — we had to find a way to reduce SO₂ emissions. This led to the invention of scrubbers for power plants — systems where gas emissions are pre-treated with alkaline water. In other words, catalytic oxidation occurs not in the atmosphere, but inside the scrubber. However, since scrubbers increase the cost of generated energy by about 30%, China, Russia, and developing countries largely avoid using them. They also rarely employ electrostatic filters designed to capture dust from emissions. And one might say this is their internal affair — if not for one inconvenient «detail»: the very same transboundary transport.

A NEW ACID IN THE RAINDROP

It might seem that the acid composition of rain is already well studied. Yet nature continues to surprise scientists. Recently, the international scientific journal Nature published data on a new acid discovered in rain. This new anthropogenic compound is called trifluoroacetic acid (TFA). It belongs to the so-called «forever chemicals» — substances with strong carbon–fluorine bonds that cannot be broken down by natural processes, allowing them to persist in the environment for an incredibly long time.

Scientists and regulatory authorities disagree on the extent of the threat it poses. TFA has been detected in lakes and rivers, bottled water and beer, cereal crops, animal liver, and even in human blood and urine. And everywhere, researchers have recorded an increase in its concentration. UN experts claim that by 2100, TFA levels will pose minimal risk. However, several governments and corporations have already called for this assessment to be reconsidered.

ENVIRONMENTALISTS SOUND THE ALARM

European environmentalists have warned that rising levels of TFA could cause irreversible damage to the planet’s «environmental boundaries». Yet the new rain-borne acid has powerful industrial lobbyists behind it — namely, the refrigeration, agrochemical, and pharmaceutical industries. The stakes are high, as regulating TFA could have far-reaching consequences for them. Opponents of the theory that TFA is anthropogenic point out that vast amounts of the acid are found in the oceans, suggesting a natural origin.

Their opponents counter that no microbial processes capable of producing such an acid are known to science. And while one might still debate the case of the oceans, the sharp increase in TFA levels on land is undoubtedly the result of human activity. Scientific data on its effects on the human body remain quite contradictory. Meanwhile, as scientists continue to argue, the concentration of trifluoroacetic acid in both our environment and ourselves keeps rising — and what it will lead to in reality, no one knows.

Original research:

There’s a new acid in our rain — should we be worried?