What makes rain smell like rain

When it comes in contact with organic debris or chemicals on the ground, it can cause some particularly aromatic reactions. It breaks apart soil and releases minerals trapped inside, which react with chemicals, such as gasoline, giving them a stronger smell.

These reactions generally produce more unpleasant smells than bacteria spores, which is why the after-the-rain smell isn't always a good one. Like the smell caused by the bacteria spores, the smell of chemical reactions is most noticeable when it rains following a dry spell. This is because once the chemicals on the ground have been diluted by one downpour, they don't have the same reaction with the rainwater.

Another after-the-rain smell comes from volatile oils that plants and trees release. The oil then collects on surfaces such as rocks. The rain reacts with the oil on the rocks and carries it as a gas through the air.

This scent is like bacteria spores in that most people consider it a pleasant, fresh smell. It has even been bottled and sold for its aromatic qualities! These are a few common rain smells, but there are also all sorts of other scents after it rains. There are lots of aromatic materials that the moisture and impact of rain can stir up, and the moist atmosphere following a downpour is particularly good at carrying these particles through the air.

So, when you talk about the after-the-rain smell with a friend, you may mean one thing while your friend is thinking of something else. You'll both agree, however, that the air has a much stronger aroma to it after a good rain.

Sign up for our Newsletter! Mobile Newsletter banner close. When a rainstorm comes after a drought, compounds from the oils—which accumulate over time in dry rocks and soil—are mixed and released into the air.

The duo also observed that the oils inhibit seed germination, and speculated that plants produce them to limit competition for scarce water supplies during dry times.

These airborne oils combine with other compounds to produce the smell. In moist, forested areas in particular, a common substance is geosmin , a chemical produced by a soil-dwelling bacteria known as actinomycetes. The bacteria secrete the compound when they produce spores, then the force of rain landing on the ground sends these spores up into the air, and the moist air conveys the chemical into our noses. Very dry periods may also slow down plant metabolism, with renewed rainfall giving it a kick start and causing plants to release a pleasant scent.

Thunderstorms have their role to play too, creating the clean, sharp scent of ozone - caused by lightning and other electrical discharges in the atmosphere. Prof Maribeth Stolzenburg of the University of Mississippi explains: "Besides the lightning, the thunderstorm and especially the rain will improve the air quality. Much of the dust, aerosols, and other particulates are rained out and the air clears.

Follow Mary on Twitter. Image source, Science Photo Library. There's actually some chemistry involved too. Wet earth. Geosmin also gives beets their distinctive earthy flavour.