Many people notice a distinct, clean scent immediately after a thunderstorm, and the answer to whether lightning has a smell is a clear yes. The electrical discharge of lightning generates a noticeable odor by altering the composition of the air. This characteristic scent is caused by a pale-blue gas called ozone, which is an allotrope of oxygen (\(\text{O}_3\)). While the smell is transient, its presence confirms a chemical reaction has occurred in the atmosphere.
The Chemistry Behind the Scent
The energy contained within a lightning bolt drives the creation of this unique atmospheric odor. A lightning strike can superheat the air along its path to temperatures soaring past 50,000 degrees Fahrenheit. This thermal energy and the electrical discharge split the stable diatomic oxygen molecules (\(\text{O}_2\)) into individual, highly reactive oxygen atoms (\(\text{O}\)).
These single oxygen atoms are unstable and quickly seek to bond with other nearby molecules. Most free oxygen atoms rapidly combine with an intact \(\text{O}_2\) molecule, forming the triatomic ozone molecule (\(\text{O}_3\)). This process is highly localized, meaning the concentration of ozone is highest near the lightning strike. The heat also facilitates the reaction of nitrogen and oxygen, creating nitrogen oxides (\(\text{NO}_x\)), which contribute to the chemical signature of the post-storm air.
Describing the Ozone Scent
The resulting ozone gas has a pungent odor, often described as sharp, clean, or slightly metallic. Many people liken the smell to chlorine bleach or the air near a high-voltage electrical device, such as a photocopier, where ozone is also generated. This sensory experience is fleeting because ozone is unstable and quickly breaks down into the more common \(\text{O}_2\) molecule in the lower atmosphere.
The name of the gas reflects its sensory signature, as the chemical was named for its odor when first isolated. The word “ozone” comes from the Greek word ozein, which means “to smell.” Christian Friedrich Schönbein isolated the gas in 1839, noting its pungent odor was the same one smelled after a bolt of lightning. The smell is strongest immediately after a storm before the wind disperses the gas and it naturally decomposes.
The Health Context of Atmospheric Ozone
It is important to distinguish between the transient ozone from lightning and ozone that is a major air quality concern. While the chemical formula is identical, location determines its effect on human health, separating beneficial stratospheric ozone from harmful ground-level ozone. Stratospheric ozone, located high in the atmosphere, forms a protective layer that shields the planet from the sun’s ultraviolet radiation.
Ground-level ozone is a harmful air pollutant and is the main ingredient in smog. This low-lying ozone is primarily created by the reaction of sunlight with pollutants like nitrogen oxides and volatile organic compounds from car emissions and industrial sources. Breathing this ozone can irritate the respiratory system, worsening conditions such as asthma and causing inflammation and reduced lung function. The low concentration of ozone created by lightning is a short-lived, natural phenomenon and does not pose the same chronic health threat as the long-term, widespread pollution from anthropogenic sources.