Ozone flare
A dangerous gas where the trend is going the wrong way
A generation ago, Britain’s city-dwellers thought of local air pollution as a problem that was on the way to being licked—the smogs of the 1950s were fading from memory. But some forms of pollution have got worse since. Ozone doesn’t sound scary: it’s made out of oxygen, and occurs naturally, especially very high up, in the “layer” that shields us from the sun’s ultraviolet rays. But this pungent gas is also created closer to the ground in reactions between sunlight and other pollutants, especially on hot still days. Urban ozone is now at almost double 1988 concentrations. The molecule, O3, has three atoms, not the usual two, which makes it unstable. It reacts with all sorts of things, including inside the body, where it causes lung problems.