Rain can clean polluted air because as it falls, it captures pollutants in the atmosphere, carrying them to the ground. This process, called 'atmospheric washing', helps improve air quality by removing some of the harmful substances.
Rain acts like a kind of natural shower for the atmosphere, capturing many pollutants present in the air as it falls. When water droplets pass through the air, they pick up fine particles or dissolved gases from pollution. Once laden with these pollutants, the droplets fall to the ground, cleansing the air of some of its impurities. This natural cleaning process helps to reduce air pollution, sometimes making the air more breathable after a heavy shower. However, it is not perfect; some pollutants resist the raindrops and persist after the shower.
When raindrops fall, they capture some polluting gases present in the air, notably sulfur dioxide (SO₂) and nitrogen oxides (NOx). These gases are soluble in water and dissolve easily, much like sugar in your coffee. Then, a portion can chemically react in the droplets to form diluted acidic substances that fall to the ground as slightly acidic rain. Even if you don't always notice it, this phenomenon significantly reduces the concentrations of these gaseous pollutants in the atmosphere during and after showers, making the air a bit more breathable.
When it rains, the droplets carry away a large part of the fine particles present in the air. These particles, often stemming from road traffic, district heating, or industrial activities, float in suspension and make the air unhealthy. As they pass through the atmosphere, the droplets capture these particles and bring them back to the ground: this is called atmospheric washing. The heavier it rains, the more effective this natural cleansing is, temporarily making the air more breathable. But beware, this phenomenon offers only a fleeting respite, as soon as the rain stops, the particles begin to accumulate again.
When heavy rains fall on cities, they tend to bring a real breath of fresh air. In fact, they capture all kinds of pollutant particles suspended in the air, such as dust, heavy metals, and residues from exhaust fumes. A good downpour can thus drastically reduce the infamous urban smog, that dirty haze we all dislike. After a heavy rain, we generally breathe better in the city, simply because the air becomes less laden, cleaner. However, it's not magical: this positive effect often remains temporary. As soon as the rain stops, especially in cases of heavy traffic or intense industrial activity, pollution levels can quickly rise again.
Rain does not perform miracles: it does not permanently clean the air. Even though it temporarily removes fine particles and certain pollutant gases, these can later end up on the ground or in watercourses. A good example is acid rain, when the captured pollutants make the rain more acidic, damaging plants, degrading buildings, or acidifying rivers. Additionally, pollutants deposited on the ground can contaminate fields or groundwater. And of course, as soon as it stops raining, the concentration of pollutants quickly rises again, especially in cities. In short, it is effective in the short term but clearly not a sustainable or sufficient solution to address air pollution problems.
Did you know that the specific smell felt after rain is called petrichor? It comes partly from chemical compounds released by the moist soil after a dry spell.
A study conducted in several major cities has shown that heavy rain can reduce the amount of fine particulate matter in the air by up to 60% in just a few hours.
The first raindrops after a dry period can sometimes temporarily increase air pollution by bringing down the pollutants that have accumulated in the upper layers of the atmosphere.
Some countries use artificial rain, also known as cloud seeding, to accelerate air purification during particularly severe pollution episodes.
Rain temporarily helps improve air quality by cleaning atmospheric pollutants. However, this does not replace sustainable solutions such as reducing pollutant emissions at the source.
Some soluble chemical pollutants can contaminate soils and waterways, impacting flora and fauna after leaching. Additionally, acid rain caused by the absorption of gases such as sulfur dioxide can damage buildings, soils, and vegetation.
The improvement is generally temporary, varying from a few hours to a few days depending on the intensity of urban traffic, industrial activities, and subsequent weather conditions.
Yes, intense rainfall often results in a more pronounced leaching effect due to better capture and removal of fine particles present in the air compared to light drizzle.
No, rain is mainly effective against fine particles and certain water-soluble gases, but some less soluble or gaseous pollutants require other natural or artificial mechanisms for removal.
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