I live in an area that is classified as having a semi-arid, tropical climate. When it rains it really rains (300mm per day sometimes) and then it doesn't rain for about 8–10 months. And when I say it doesn't rain I don't mean there's a bit of drizzle, I really do mean it doesn't rain: zero, zilch, naught. However we do get really heavy dew. When I first move here I would hear what I thought was rain and would look up to see thousands of stars twinkle at me as if to say "What! Nothing to see here." I should have cottoned on because it always happened at night but no, it took a good few months to work out that it was actually dew condensing on the roof and beams and then falling in large drops to the ground.

Anyway, I digress (not having actually got to my point yet!). I recently said to a friend the petrichor smells amazing at the moment and she looked at me quizzically and said can you still call it petrichor when it's not raining? Which is a fair question and one which this blog post attempts to answer.

Petrichor, if you're not familiar, is:

A pleasant, distinctive smell that frequently accompanies the first rain after a long period of warm, dry weather in certain regions ... — Oxford English Dictionary, 2nd Edition

So the OED says rain but what does petrichor actually mean? For that we need to look at where it was first coined which is a 1964 paper published in Nature¹ where is says:

… led us to propose the name "petrichor" for this apparently unique odour which can be regarded as an 'ichor' or 'tenuous essence' derived from rock or stone.

Alrighty no mention of rain. They go on to explain their experimental method:

To obtain sufficient petrichor for examination and analysis source materials in amounts of 2-3 kg were exposed to daylight and the atmosphere but protected from rain.

Interesting, they specifically excluded rain! That said they do use rain twice in the introduction:

… this odour is most widely recognized and is frequently associated with the first rains after a period of drought. There is some evidence that drought-stricken cattle respond in a restless manner to this "smell of rain" which may drift with the wind for considerable distances.

but this is the only part of the paper where the authors use it.

So after all that I'm calling it! It's ok to use petrichor in conjunction with dew.

[1] Bear, I., Thomas, R. Nature of Argillaceous Odour. Nature 201, 993–995 (1964)