The smell of rain on a hot day

Some people dance in the rain. Others just get wet.

I can’t find who first said this. Seems that it is a tweak on Bob Marley “Some people feel the rain…”. It has always resonated with me and was brought to mind by this mornings deluge. Yes, by the standards of most parts of the world it was a little shower, but by San Diego standards…massive.

I just adore the smell of rain on a hot day. That afternoon shower that comes through, and clears the air and leaves a sticky warmth and a wonderful unique odor. The hard rain that usually precedes this lovely smell is so heavy, it is just begging for you to run outside, splash in the puddles and to slide on the grass. 

So what is the smell? And why do we all love it so? 

A couple of Australian scientists (Isabel Joy Bear and R. G. Thomas) published an article in Nature titled “Nature of Agrillaceous Odor.” that described the results of their research into this unique odor. They decided to call the smell petrichor [petra (stone) and ichor (the blood of gods in ancient myth)].

It seems that a unique blend of oils, excreted by plants during dry spells and absorbed by rocks and soil, are mixed with the water and released into the air. These oils the combine with substances such as geosmin and actinomycetes (a chemical produced by a soil-dwelling bacteria). Produced in dry spells the bacteria tend to collect in the soils until they are liberated by the rain. (Incidentally, geosmin is also responsible for the earthy taste in beets… no wonder I love them!)

Then there is the psychological element of why we like the smell of petrichor so much. An Australian anthropologist Diana Young has observed that the  Pitjantjatjara people of Western Australia associate the smell with the color green. I guess since they live in the desert, there is almost an instant transformation of an arid landscape to a blooming paradise in a matter of days. With it comes life and food. 

I wonder if any branding/marketing companies have picked up on this yet and tried to synthesize it to promote a green brand? Drawing on innate human instincts of joy would seem like an instant winner. 


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