Many people claim they can “smell a storm coming,” a notion with a scientific basis. Distinct odors become more noticeable before or during a storm, produced by specific chemical processes and environmental shifts.
The Science of Storm Odors
One smell associated with an approaching storm is a sharp, clean scent, sometimes described as similar to bleach. This odor is ozone (O3), formed when lightning discharges electrical energy into the atmosphere. Lightning splits oxygen molecules (O2) into individual atoms, which then combine with other O2 molecules to create ozone. Ozone’s distinctive smell can travel on air currents, reaching noses before the storm arrives.
Another common storm-related scent is petrichor, an earthy, musky aroma occurring when rain falls on dry soil. This scent is caused by plant oils and geosmin. During dry periods, plants release oils that accumulate on surfaces, and soil bacteria (Streptomyces coelicolor) produce geosmin.
When raindrops hit dry ground, they trap air bubbles that burst, aerosolizing accumulated plant oils and geosmin. This process releases the compounds into the air, creating petrichor’s characteristic scent. Geosmin is particularly potent, detectable at concentrations as low as 5 parts per trillion.
How Atmospheric Changes Influence Scent Perception
Atmospheric conditions before a storm enhance odor perception. Increased humidity, common before rain, plays a significant role. Water molecules in humid air bind to odor compounds, allowing them to travel more efficiently and become more concentrated, making them more detectable.
A drop in barometric pressure, a common precursor to stormy weather, also contributes to heightened scent perception. As atmospheric pressure decreases, gases and compounds trapped in the ground or other surfaces can be released more easily into the air, increasing their concentration. Changing air currents and updrafts further distribute these airborne scent molecules, allowing odors to travel from their source to wider areas.
The Limits of Our Noses and Other Indicators
While smelling a storm is possible, relying solely on scent for prediction has limitations. Odor intensity depends on factors like storm type, proximity, and individual sensitivity. Not all storms produce strong, easily detectable odors, and their strength varies significantly.
People often combine the sense of smell with other sensory cues to anticipate an approaching storm. Visual indicators include the darkening of skies and the formation of specific cloud types, such as towering cumulonimbus clouds, which are characteristic of thunderstorms. Auditory cues also provide valuable information; distant thunder, even if barely audible, or changes in wind sounds can signal an impending weather event. Physical sensations can also contribute to a holistic “storm sense,” including a noticeable change in temperature, a feeling of pressure in the ears due to barometric shifts, or even the sensation of static electricity in the air. Animals, with their heightened senses, often display behavioral changes like increased anxiety or seeking shelter, which can also serve as indicators of an approaching storm.