A rainbow might accompany the distinctive scent after a rain shower. |
Distinctive Smell After It Rains
What causes the smell
after rain?
Most
people notice a distinctive smell in the air after it rains.
It's
frequently linked with spring, as the smell of fresh cut grass is
associated with summer.
You'll
find it in a lot of poetry and also on many inspirational lists of things to be
happy about. But what causes it?
As
it turns out, the smells people associate with rainstorms can be caused by a
number of things.
One
of the more pleasant rain smells, the one we often notice in the woods, is
actually caused by bacteria!
Actinomycetes, a type of filamentous bacteria, grow in soil when
conditions are damp and warm.
When
the soil dries out, the bacteria produces spores in the soil.
The
wetness and force of rainfall kick these tiny spores up into the air where the
moisture after a rain acts as an aerosol (just like an aerosol air freshener).
The
moist air easily carries the spores to us so we breathe them in.
These
spores have a distinctive, earthy smell we often associate with rainfall.
The
bacteria is extremely common and can be found in areas all over the world,
which accounts for the universality of this sweet "after-the-rain"
smell.
Since
the bacteria thrives in moist soil but releases the spores once the soil dries
out, the smell is most acute after a rain that follows a dry spell, although
you'll notice it to some degree after most rainstorms.
Another
sort of smell is caused by the acidity of rain.
Because
of chemicals in the atmosphere, rainwater tends to be somewhat acidic,
especially in urban environments.
When
it comes in contact with organic debris or chemicals on the ground, it can
cause some particularly aromatic reactions.
It
breaks apart soil and releases minerals trapped inside, and it reacts with
chemicals, such as gasoline, giving them a stronger smell.
These
reactions generally produce more unpleasant smells than bacteria spores, which
is why the after-the-rain smell isn't always a good one.
Like
the smell caused by the bacteria spores, the smell of chemical reactions is
most noticeable when it rains following a dry spell.
This
is because once the chemicals on the ground have been diluted by one downpour,
they don't have the same reaction with the rainwater.
Another
after-the-rain smell comes from volatile oils that plants and trees release.
The oil then collects on surfaces such as rocks.
The
rain reacts with the oil on the rocks and carries it as a gas through the air.
This
scent is like the bacteria spores in that most people consider it a pleasant,
fresh smell. It has even been bottled and sold for its aromatic qualities!
These
are a few common rain smells, but there are also all sorts of other scents
after it rains.
There
is lots of aromatic material that the moisture and impact of rain can stir up,
and the moist atmosphere following a downpour is particularly good at carrying
these particles through the air.
So,
when you talk about the after-the-rain smell with a friend, you may mean one
thing while your friend is thinking of something else.
You'll
both agree, however, that the air has a much stronger aroma to it after a good
rain.
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