2. Ozone measurement

2.1 Ozone properties

Ozone is a common species in the free atmosphere, present at concentrations ranging from 40-50 ppbv in March-April to around 30 ppbv in July. The ozone minimum in July is due to the fact that, at this time of year, ozone precursors no longer reach the free atmosphere, as they are largely transformed in the lower layers when photolytic ozone destruction is at its peak. On the contrary, in the lower troposphere in continental areas, rural ozone concentration is highest in summer, 50 to 60 ppbv in eastern France, and lowest in winter, 10 to 20 ppbv. In the plume from sources, and under certain conditions in cities (stagnation, recirculation), ozone concentrations in France can reach over 100 ppbv, and sometimes over 200. Ozone reacts rapidly with soil, vegetation...