Weathercatch: If rain has no scent, what was that splendid smell on Aug. 6?

One week ago today, many of us awoke to see raindrops tapping on windows and the ground outside. It didn’t amount to much precipitation – only .02 of an inch in Spokane, .04 of an inch Moscow-Pullman and .10 of an inch in Deer Park. But wow, did it smell pleasant.

The unique scent of mossy earth combined with fresh-cut grass permeated the air. Contrary to what many people may have thought, it wasn’t the rain itself that smelled so good. It’s just water, after all. Instead, it was a chemical compound released when rain fell after a 36-day dry spell in our region.

The word for it is almost as intriguing as the fragrance: petrichor.

Named by two Australian researchers in 1964, the term is derived from the Greek “petra,” which means stone, and “ichor” which refers to the ethereal blood of the gods in Greek mythology. In a paper published in the journal Nature, the scientists were the first to document the process of how this heady potpourri comes about.

Until then, the general belief was that this widely known and revered phenomenon was simply the smell of rain. But as the influential study revealed, rain is but one of the vital ingredients necessary to produce it. Hot, dry ground is another key ingredient.

Before the morning of Aug. 6, the Inland Northwest had plenty of it. On top of near record-breaking heat in late July, no measurable precipitation had fallen in Spokane and other locations since July 1.

Then, as rain drops finally hit the ground, they interacted with dry dirt and vegetation, creating a brew of soil-dwelling bacteria and plant oils called geosmin. Although we received only a small amount of rainfall, it was enough to flush this organic compound into the air as a pleasant-smelling aerosol, which, luckily for us, was carried through the air by a light breeze.

Had the rainfall been heavier, the scent could have wafted downwind and alerted people that rain was heading their way. If you’ve ever smelled an oncoming summer rain, that’s why.

Whether or not you have a nose for weather, it may be a while before you catch your next whiff of petrichor. Late summer is historically a very dry time of year in the Inland Northwest. And considering the current forecast favors even drier-than-normal conditions, rain will likely be scarce in the coming weeks.

When it does return, you might step outside and inhale a scent so special that perfume makers keep trying to reproduce it to sell in a bottle.