Map showing the distribution of surface ozone around the world. Brighter areas have a higher concentration of ozone. While ozone in the stratosphere protects us from the Sun's ultraviolet radiation, lower down in the atmosphere it is a harmful pollutant. Ground level ozone is created by chemical reactions between oxides of nitrogen and volatile organic compounds in the presence of sunlight. The highest concentrations of surface ozone are found in the afternoon around cities due to human activity.