Studies into the effects of negative ions on mood began in the 1950s, though results were inconclusive until more advanced, high-voltage ionisers that more efficiently produced negative ions became available in the 1990s. In one notable 1995 study, researchers found that participants with seasonal affective disorder (Sad) who were given daily sessions with high-voltage ionisers were far more likely to see a large reduction in their symptoms than those given a low-output treatment.
According to Columbia University professor Michael Tehan, who led the study, heavy rain produces similar levels of negative air ions to the high-voltage ionisers used by his team. He notes, though, that so far no study has directly demonstrated this, nor directly correlated time in the rain with mood changes.
The cleaner air
Rain’s negative ions also appear to clear the air of particulate matter such as pollution and allergens, making it easier to breathe. This could have an impact on mood and health as well: since poor air quality is associated with increased anxiety and risk of developing more severe mental health disorders, it stands to reason that cleaner air would promote the opposite.
“There is reasonably good evidence that the negative ions can clear dust, bacteria, allergens, and other particles from air, which for many can have a positive effect on respiratory health,” says Dalton.
Water sounds have been associated with activation of the parasympathetic nervous system, the branch of the nervous system involved in relaxation and recovery – Amy Sarow
Just how adept negative ions are at cleaning was less clear until about a decade ago. In a 2015 study, researchers replicated this ability in miniature by pumping different kinds of particulate matter into a raindrop-generating glass chamber. After the raindrops had evaporated, researchers collected the remaining particles, noting their position to determine whether the raindrops had, in fact, attracted them. They found that smaller raindrops were particularly adept at attracting these airborne particles.
When raindrops fall to the ground, they’re essentially “sweeping up” tiny airborne particles in their path, says Dan Cziczo, co-author of the study and a professor of earth, atmospheric and planetary sciences at Purdue University in Indiana in the US. The electrical charge (the ions) within a raindrop acts like a magnet for these particles, resulting in a sweeping-up process known as coagulation.
Cziczo likens it to what happens when a construction crew sprays a dusty site with water; the suspended dust is pushed back down to the ground, leaving the air cleaner.
The intensity of the rain also matters. “The heavier the rain, the more of a cleaning effect you’re going to get on the atmosphere,” says Cziczo. This includes reducing the amount of positive air ions, which have been associated with irritability and heightened anxiety.
So next time there’s a heavy rainfall, consider opening your windows right after it stops. You’ll likely notice the air seems clearer, and if it came on the heels of a cold front (as heavy rains often do), the accompanying wind may blow some of that clean air into your home, improving the air quality.
