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The Aromas of Spring

March 8, 2021

Following a harsh February during a winter where everyone felt cooped up more than usual, the recent sunshine and warmer weather have certainly provided a morale boost for many of us. Spending time outside after a period of relative hibernation really wakes up one's senses. Color returns to the earth, warmth to our skin, and along with it nature provides some unique aromas for us to enjoy. Where do these earthy smells come from?

We have all been outside following or leading up to a rain shower and smelled a very pleasant odor that may very well remind us of spring. This aroma actually has a name: petrichor. The smell of petrichor, which is usually stronger following drier weather, is caused by a combination of chemical reactions that comes with the moisture. During dry weather, plants secrete oils that accumulate and are then released into the air when it rains. We are also smelling a compound called geosmin, which is secreted by bacteria in the soil when it comes in contact with raindrops. Lastly, if the showers are accompanied by lightning, it too can play a role in petrichor, as it will bring with it ozone from our atmosphere. Some may describe this fragrance as clean, which makes sense as the showers help dust and other aerosols settle, making the air feel refreshing. Humans are particularly sensitive to these aromas, and aside from rain, many of us will enjoy these odors when we first dig into our garden or till a field. This is also caused by bacteria in the soil releasing compunds, including the aforementioned geosmin. Interestingly, how our soil smells can actually be an indicator of how healthy it is. Soils should smell clean and pleasant, whereas soils that are poorly drained and lack oxygen will smell sour, sometimes almost like ammonia.

We are a few weeks away from the smell of flowers in the air, but that lovely fragrance will be arriving soon as well. Why do flowers emit a pleasant odor? Much like we are attracted to their scent, so too are the pollinators, such as insects, bats, and bees that they need to reproduce. Flowers are more fragrant during some times more than others, as they are letting their pollinators know that they are ready for fertilization. This scent comes from essential oils that are stored in the flower's petals.

As beautiful as the interaction between flower and pollinator can be, another perfume of nature is actually a plant's cry for help: the smell of fresh-cut grass. When injured, many plants, grass included, release a distress signal. These aromatic chemical compounds that are released serve a few functions such as formulation of new plant cells, and even healing chemicals, similar to the way an antibiotic works. Some research even suggests that this odor signals to birds and other insects to please come and eat the pest that is harming me!

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