Ozone is a toxic bluish unstable gas, with a pungent odour and is highly reactive. It is the tri-atomic form of molecular oxygen.
Sources
It occurs naturally in the atmosphere, particularly in the stratosphere (about 19-30km above ground level), where it acts as a filter against incoming ultraviolet radiation from the sun and is known as the Ozone layer. Lower down at ground level it is formed by volatile organic compounds (VOC’s) and nitrogen oxides (NOx) in the presence of sunlight. VOC’s and NOx in the UK are mainly produced by motor vehicles. Concentrations within the UK vary, they tend to be higher around the coast. The highest concentrations occur in rural areas. Seasonal variations also influence concentrations, peaking in the spring whilst the lowest concentrations are in the autumn.
Health
On the one hand ozone in the stratosphere protects us from potentially dangerous ultra-violet (cancer causing) radiation. Lower down it acts as an irritant to the respiratory system and can impair lung function. Asthma sufferers are particularly susceptible.
