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Infographic Contest Winner
2 ChemMatters | FEBRUARY/MARCH 2017
Connect with acschemclubs on:
What Is Petrichor?
The term petrichor was coined by Australian scientists in 1964
to describe the unique, earthy smell associated with rain.
It is caused by rainwater falling on dry soil, along with
certain compounds like ozone, geosmin, and plant oils.
A type of bacteria found in soil,
known as actinomycetes,
secrete a compound
called geosmin, which is
released from soil into
the air by raindrops. The
human nose can detect
geosmin in the air at less
than five parts per trillion.
Stearic Acid C18H36O2
Palmitic Acid C16H32O2
During a lightning strike, diatomic molecules
of oxygen and nitrogen (containing two
atoms) are split and re-arranged to create
nitric oxide (NO) and ozone (O3). Ozone
molecules are carried down by
raindrops to contribute to the scent.
Stearic acid and palmitic acid are two such
compounds. They are fatty acids— long
hydrocarbon chains with a carboxyl
group on one end and a methyl
group on the other end.
During dry weather, plants produce compounds that
accumulate between rocks and in soil. When it rains,
these compounds, called volatile plant oils, are released
into the air to add to the earthy smell of petrichor.
Ozone & Lightning
Volatile Plant Oils
R C H
The word petrichor sounds like an answer you would
Prunier from Guilderland High School in Guilderland
Center, N. Y., created this month’s winning infographic
to teach us more about the chemistry of petrichor, the
smell that greets us as we step out, umbrella in hand,