[Hadrian (OP)]

The weather report on the radio or TV tells you that it is going to be sunny and hot and that an ozone alert has been issued. What is ozone? What does an alert mean? Why should you be concerned about it?   [^]

[ROBERT]

Ozone is a molecule of Oxygen which has three atoms instead of the usual two.

Ozone high in the atmosphere protects life from harmful UV radiation from the sun.

Ozone at low levels is poisonous to life.

In the stratosphere, ozone shields us from the Sun’s deadly ultraviolet radiation.
 But in the troposphere, this same gas impairs lung capacity and reduces agricultural productivity.

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16278

The ozone warnings are targeted at those with lung diseases, e.g. asthma,
who could take more medication for their condition when ozone levels rise.

[JimBob]

Ozone also breaks down tire (tyres) on bycicles and autos, and other anodized rubber products.