Petrichor

As I was walking out of work on Monday, I was greeted by one of my favourite things – this:

The Royal School of Mines in the rain

The Royal School of Mines in the rain

On first glance you may think, “wow, what a miserable sky.” What you also need to know is that this grey blanked overhead full of heavy rain clouds followed three days of hot, sunny, dry weather. The heavens had just opened, breaking the short but very warm dry spell with a torrential downpour of huge raindrops. What greeted me and blew me away as I left work was not the grey sky as such, but what it had produced – the heady aroma of petrichor in the air.

The Royal Albert Hall in the rain

The Royal Albert Hall in the rain

Petrichor is one of my favourite words, and one of my favourite things. It is the word that sums up the smell of wet rain on dry ground after a long period of dry weather. It is the scent of summer storms – the kind of weather where you can run through the heavy rain in a t shirt – sadly the kind of weather we rarely have a chance to enjoy here in England. Sometimes I think I can detect a delicate note of petrichor in the peaty, smokey flavours of my favourite whisky, Laphroaig. I imagine that petrichor is that same earthy perfume that filled the air when George Peppard rather romantically kissed Audrey Hepburn after she rescued Cat, or when Hugh Grant  kissed Andi McDowell in Four Weddings. Was it still raining? She hadn’t noticed. It must have been warm leading up to that summery shower, as we had Hugh Grant getting soaked to the point of see-through in a white shirt, and no one would do that in winter. OK, it may instead have been because Richard Curtis knows how women respond to men in soggy white shirts, but I like to presume the former, as I feel a little less manipulated that way!

Paul Varjak and Holly Golightly kiss in the rain while protecting a freshly rescued Cat in one of my all time favourite films (via Breakfast at Tiffany's)

Paul Varjak and Holly Golightly kiss in the rain while protecting a freshly rescued Cat in one of my all time favourite films (via Breakfast at Tiffany’s)

'That kiss' (via Four Weddings and a Funeral)

‘That kiss’ (via Four Weddings and a Funeral)

I first came across the word ‘petrichor’ in Neil Gaiman’s book American Gods, and always remembered it because it is a scent that everyone is familiar with, and everyone has their own description of, yet very few people know what word to use to sum it up. Gaiman later used the word again in one of the excellent episodes of Doctor Who that he wrote entitled ‘The Doctor’s Wife’, where a conjured memory of the scent of rain on dry earth was used as a telepathic passkey to enter a TARDIS control room. It was also the name of Amy Pond’s perfume in a later episode, ‘for the girl who’s tired of waiting’.

An advert for Amy's perfume, Petrichor, from Doctor Who (via BBC)

An advert for Amy’s perfume, Petrichor, from Doctor Who (via BBC)

A few weeks ago I attended a choral performance of a composition documenting Alan Turing’s life. While they referred to the very same scent in the lyrics, they didn’t use the word ‘petrichor’, presumably because the composer didn’t feel like it fit in the lyrics or the melody. I can’t imagine he would have let such a beautiful word go easily. While the meaning was still the same, it didn’t invoke the same response in me as petrichor would have. When I hear the word, my mind immediately visualises a single rain drop falling in slow motion until it reaches the dry earth, where a small cloud of dust is propelled into the air above the rain drop on impact.

Despite only having heard the word via Neil Gaiman in the last few years, it has been around for a long time, and was originally coined by two academics working on the composition of this scent from a scientific point of view. The word is constructed from Greek ‘petros’ meaning ‘stone’ or ‘soil’ and ‘ichor’ which is the fluid that flows like blood in the veins of Greek gods.

Researchers have identified what this scent is, and how it comes about thanks to the combination of a warm, dry spell followed by torrential rain. During the dry spell, plants start to release oils into the soil around them that slow down seed germination and the growth rate of plants, as they rather cleverly realise that there may not be enough water for them to grow properly if it is very warm. When the rain starts to fall, the soil is agitated, and these oils mix with other chemical products from certain bacteria that live in the soil. This combination of chemicals released in the soil and mobilised by the rain evaporate off the ground and into the air around, creating the smell of rain on dry ground. Petrichor.

Not only is petrichor a beautiful word, it is also a wonderfully emotive scent, and the result of a clever mechanism that enables plants to respond to their sometimes unpredictable environmental conditions and survive in spite of these challenges.

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