Though many springtime smells are familiar, what produces the scents of the season might surprise you. Here are a few of common odors and their unusual origins.
Bouquet of roses: Of all the springtime smells, that of blooming flowers may be the most welcome. These plant perfumes are tiny molecules called volatile compounds, released from various parts of the plant skins, petals and stems. Though humans have long known about flower scents — the distillation of rose oil dates back to medieval medicine in Persia — scientists are still untangling the reasons why flowers smell. “Perhaps the greatest mysteries surrounding volatiles concern their function in the life of the plant,” wrote a group of molecular biologists in a 2004 review. Various experiments suggest that flowers use their smells to attract insects or ward off plant-eaters, and may, in the case of a rose's phenethyl alcohol, boast antimicrobial properties.
The scent of rain: People who sniff out a storm before it arrives are catching a whiff of ozone. When a storm discharges electricity via lightning, this can sever oxygen molecules into its constituent atoms. These atoms form ozone, which when blown down from the atmosphere may herald a coming storm. And what about the scent of rain as it hits the ground? There's a name for that scent, called petrichor, which is the smell of an oily substance produced by wet rocks. Raindrops that fizz as they splash down carry the aroma of petrichor, as well as bacteria and other organic matter, up to our noses.
Fresh grass fragrance: You might be fond of the smell of cut grass, but it's a plant cry for help. Sliced leaves release compounds to indicate they're distressed, which can summon defenders — such as parasitic wasps that lay their eggs on caterpillars that eat plants.
Stinky cities: The weather might be pleasant, but not everything smells so sweet. City-dwellers have come to loathe the smell of the Callery pear tree, a Chinese tree that became popular for its white petals and hardy growth. But it produces a scent frequently likened to, um, semen. (The city of Pittsburgh's urban forest program now bans planting the Callery pear.) The tree's rancid stench, one Cornell University botanist theorized in 2013, could attract insects like flies. Or it might deter other invertebrates from slurping too much of the tree's nectar.
Smell of a beach: Perhaps you escaped a smelly city for an early beach visit, only to be greeted by a sulfuric tang. That's dimethyl sulfide, a volatile chemical produced by oceanic algae when the algae die. As a University of Delaware marine scientist told Wired in 2015, the dimethyl sulfide is a warning signal to other algae — and also serves as a dinner bell for small fish.