Atmospheric Aromatherapy The Smell of Rain

Many people claim they can smell a storm coming (meaning they can sense when bad luck is headed their way), but did you know that this weather expression also has literal meaning? Its true, there are some kinds of weather that actually do produce a unique smell, and were not just talking the smell of flowers in spring.  Based on personal accounts, here are some of the weathers recurring aromas, plus, the scientific reason behind them.   When Rainstorms Wet Dry Earth Rainfall is one of natures most  soothing sounds, but its also behind one of the weathers most pleasing smells. Described as an  earthy scent, petrichor is  the aroma that arises when raindrops fall onto the dry soil. But, contrary to belief, it isnt the rainwater that youre smelling. During dry spells, certain plants secrete oils that become attached to the soil, rocks, and pavement surfaces. When it rains, the falling water disturbs these molecules and the oils are released into the air along with another soil inhabitant;  a naturally occurring chemical called  geosmin  thats  produced by fungi-like bacteria.   Had a recent rainstorm, but didnt have the  lingering petrichor afterward? How strong the scent will depend on several things, including how long its been since the last rainfall and  rainfall  intensity. The longer the geosmin and plant oils are allowed to accumulate during periods of dry weather, the stronger the scent will be. Also, the lighter the rain shower, the stronger the petrichor scent, since lighter rains allow more time for the grounds scent-carrying aerosols to float. (Heavier rains keep them from rising up as much into the air, which means less smell.)  Ã‚  Ã‚  Ã‚   Chlorinated Clashes of Lightning If youve ever experienced a lightning strike thats too-close-for-comfort or stood outdoors just before or after a thunderstorm, you may have caught a whiff of another rain-related scent;  ozone (O3). The word ozone comes from the Greek  ozein  meaning to smell, and is a nod to ozones  strong odor, which is described as a cross between chlorine and burning chemicals. The smell doesnt come from the thunderstorm itself, but rather, the storms lightning. As a bolt of lightning travels through the atmosphere, its electrical charge splits airs nitrogen (N2) and oxygen (O2) molecules apart into separate atoms. Some of the lone nitrogen and oxygen atoms recombine to form nitrous oxide (N2O), while the leftover oxygen atom combines with an oxygen molecule in the surrounding air to produce  ozone. Once created, a storms downdrafts can carry the ozone from higher altitudes to nose level, which is why youll sometimes experience this smell before it starts storming or after the storm has passed.  Ã‚   Unscented Snow Despite some peoples claims that they can smell snow, scientists arent entirely convinced. According to olfactory scientists like Pamela Dalton of Philadelphias Monell Chemical Senses Center, the smell of cold and snow isnt so much about a particular smell, its more about the absence of smells, as well as the noses ability to sense that air is cold and moist enough for the weather to possibly turn snowy. Were not as sensitive to odors in winter... and odors arent as available to be smelled, Dalton says. Not only do smells not waft as easily when air is cold, but our noses dont work as well. The smelling receptors within our noses bury themselves more deeply within our nose, likely as a protective response against the colder, drier air. However, when cold air becomes more humid (as it does before a snowstorm), the sense of smell would sharpen ever so slightly. Its possible that we humans link this small change in smell  to an oncoming snowstorm and hence, why we say we can smell snow. Crisp, Clean Autumn Air Like winter, autumns crisp, clean smell is partially thanks to the drop in air temperature which suppresses strong odors. But another contributor is  autumns hallmark symbol; its foliage. Although leaf peepers are disappointed  when falls brilliant crimsons and golds fade to grayish-brown, this is when leaves take on their sweetest smell. During the autumn season, a  trees cells begin the process of sealing off its leaves in preparation for winter. (During winter, temperatures are too cold, sunlight too dim, and water too scarce and susceptible to freezing to support growth.) A corky barrier is formed between each branch and each leaf stem. This cellular membrane blocks the flow of nutrients into the leaf.  As leaves are sealed off from the rest of the tree and lose moisture and nutrients they begin  drying out and are further dried by autumns sun and lower humidity. When they fall to the ground, they begin to decay; that is, theyre broken down into essential nutrients. Also, when leaves are brown it means theyre carbon-rich. The dry, decomposition process gives off a mildly sweet, almost floral-like aroma.   Wondering why the leaves in your yard dont smell as sweet in other seasons? Its largely because theyre full of moisture and are  nitrogen-rich. An abundance of moisture, nitrogen, and improper aeration generates pungent, rather than sweet, odors.   Tornadoes Terrible Sulphur Scent Most of us are familiar with the sound a tornado makes, but what about its accompanying smell? According to a number of storm chasers, including the late Tim Samaras, the air sometimes smells of a mix of sulfur and burning wood (like a freshly lit  match) during a tornado. Researchers havent determined why this is a recurring smell with observers. It could be from broken natural gas or sewage lines, but no one knows for sure.  Ã‚   In addition to sulfur, others report  the smell of fresh-cut grass during a tornado, likely as a result of tornado debris tearing tree limbs and leaves, and of the storm itself uprooting trees and turf. Which smell you get depends on how close you are to the tornado, how strong of a twister it is, and what objects  it destroys.  Ã‚  Ã‚   Eau de Exhaust   Temperature inversions are another weather phenomenon linked to atmospheric odors,  but rather than trigger a certain smell, they exacerbate odors that are already airborne. Under normal circumstances, air temperature decreases as you move from the ground up.  However, under an inversion, this is reversed and air near the ground cools faster than that a few hundred feet above it.  This setup of relatively warm air overlying cooler air means the atmosphere is in a stable configuration, which, in turn, means there are little wind and mixing of air. As the air sits motionless and stagnant, exhaust, smoke, and other pollutants build up near the surface and hang in the air we breathe. If youve ever been under an  air quality alert in summer, an inversion (and the presence of high pressure domed over the region) is likely the cause.   Similarly, fog can sometimes hold a light smoky smell. If gasses or dirt particles are suspended in the air and weather conditions are right for moisture to condense onto them, these pollutants essentially dissolve into the water droplets and are suspended in the air for your nose to breathe them in. (Such an event is different from smog, which is a dry cloud of smoke that hangs in the air like a thick fog.)   Your Nose vs. Your Forecast   While being able to smell the weather may mean your  olfactory system is as acute as they come, take care not to depend solely on your sense of smell when sensing your weather risk. When it comes to forecasting approaching weather, meteorologists are still a nose above the rest.