After weeks of Costa Blanca heat, the first drops of September rain can bring something many of us notice almost immediately: that unmistakable smell of wet ground.
It can appear before there has been enough rain to properly soak the pavement. And despite what our noses might tell us, we are not actually smelling the rain itself.
The familiar earthy scent has a name, petrichor, and it comes from a mixture of compounds released from dry ground when rain arrives.
What exactly is petrichor?
Scientists Isabel Joy Bear and Richard Thomas coined the term petrichor in 1964 while studying why dry rocks and soils produced a distinctive smell after becoming wet.
The name comes from the Greek words for stone and ichor, the substance that Greek mythology described as flowing through the veins of the gods.
During dry periods, compounds from plants and microorganisms can accumulate in soil and porous surfaces. When moisture returns, some of them escape into the air.
That helps explain why the smell can seem particularly strong after a long, dry Costa Blanca summer.
A tiny amount can make a big smell
One of the important ingredients is geosmin, a compound produced by microorganisms in the soil, including Streptomyces bacteria.
Humans have an extraordinarily sensitive nose for it. We can detect geosmin at concentrations below ten parts per billion.
So it does not necessarily take a downpour to produce that familiar earthy smell. A relatively small amount of rain hitting dry ground can be enough.
There is another reason those first few drops can make such a difference.
Raindrops become tiny sprayers
Researchers at the Massachusetts Institute of Technology used high-speed cameras to study what happens when raindrops hit porous surfaces.
They found that a falling drop can trap tiny air bubbles when it hits the ground. Those bubbles rise through the drop and burst at the surface, releasing microscopic particles called aerosols into the air.
Those aerosols can carry some of the compounds responsible for petrichor straight towards our noses.
Interestingly, light or moderate rain can sometimes produce the effect more efficiently than a very heavy downpour.
Why it is so noticeable on the Costa Blanca
After a long spell of dry weather, there has been plenty of time for these compounds to accumulate.
That makes the first autumn showers particularly good at producing petrichor, whether you notice it while walking through the countryside, sitting in a garden or stepping outside onto a recently dampened street.
The smell can vary from place to place too. Soil, vegetation and the surface beneath the rain all influence what reaches the air.
A country track, mountain path and city pavement therefore will not necessarily smell the same after a shower.
So, next time the clouds finally open after a long Costa Blanca dry spell, there is a little more going on than rain hitting hot ground. That familiar scent is chemistry, biology and a surprisingly clever bit of raindrop physics all happening beneath your feet.
Bridging the Gap’s recap
- The familiar smell after rain is known as petrichor.
- Scientists Isabel Joy Bear and Richard Thomas coined the term in 1964.
- Dry periods allow compounds from plants and microorganisms to accumulate.
- Geosmin is one of the substances responsible for the earthy smell.
- Humans can detect extremely small concentrations of geosmin.
- Raindrops can release tiny aerosols when they hit porous surfaces.
- Light or moderate rain can sometimes produce the effect particularly well.
- Soil, vegetation and different surfaces can all change how petrichor smells.
Enjoy more Costa Blanca weather news.
