What does rain smell like

The researchers steam-distilled rocks to reveal a yellow oil that was trapped in the rocks and soil, which they said responsible for the smell. According to the Met Office, the oil is a combination of oils emitted by plants and chemicals released from bacteria in the soil.

The scent is usually the strongest as it begins to rain, although it can be detected just before it begins in some cases. Drops of rain that land on dry sandy or clay soils can trap air bubbles on the ground. Those tiny bubbles are then are thrown upward and burst out of the raindrop into the air -- a process the Met Office likened to bubbles in a glass of Champagne.

Researchers at the Massachusetts Institute of Technology examined this process in a study using high-speed camera to watch raindrops hit the ground. The MIT study found that more aerosols were produced during light to moderate rain, fewer in heavy rain.

According to information from the National Weather Service, petrichor can be most noticeable when it rains after a long dry spell on a hot day. That's because the drier the soil, the greater the buildup of plant oils and bacteria spores on the ground.

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According to Prof Nielsen, research also indicates that geosmin could be related to terpenes - the source of scent in many plants. 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.