The zonal distribution shows a peak at the surface around the
equator where there are large emissions of VOCs from forested
areas and high levels of photochemical activity. The RO2 abundances
are found to decrease with altitude (Fig. 1b).
The twelve surface measurement campaigns selected for analysis
are shown in Table 2. The seasonal variation of the peroxy
radical surface concentration of the stations situated in the
Northern hemisphere showed that RO2 abundances are at their
highest during the summer months, reaching maximum levels in