The metallic scent you smell after a thunderstorm is actually ozone.

The distinct aroma associated with thunderstorms is primarily caused by the formation of ozone, a triatomic form of oxygen. When lightning discharges, it creates a high-energy environment that severs the strong double bonds of diatomic oxygen (O2) molecules in the atmosphere. These free oxygen atoms quickly bond with remaining O2 molecules to create O3, or ozone.This process occurs during the massive electrical discharge of a lightning bolt, which can reach temperatures of approximately 30,000 Kelvin. This temperature is five times hotter than the surface of the sun, providing more than enough energy to trigger the chemical transformation. While ozone is vital in the upper stratosphere for blocking UV radiation, ground-level ozone produced by storms is what we perceive as a 'clean' or 'metallic' scent.Human olfactory sensitivity to ozone is remarkably high, as documented by researchers at institutions like the National Oceanic and Atmospheric Administration (NOAA). Most people can identify the scent at concentrations between 10 and 50 parts per billion. This evolutionary sensitivity may have served as an early warning system for approaching dangerous weather.The term was officially coined in 1839 by German-Swiss chemist Christian Friedrich Schönbein. He noticed the same smell during his electrolysis experiments and named it after the Greek word for 'to smell.' Interestingly, the scent of a storm can also include 'petrichor,' which is the earthy smell of rain hitting dry soil, but the sharp, electric tang is purely ozone.