The modelled data were monthly averages for the year 1998
which were compared with the selected field measurement data
recorded in the equivalent months of their respective campaign
years. Most of the measurement data were published as a combination
of both HO2 and RO2, so we calculated the concentrations of
HO2 þ RO2 from STOCHEM-CRI and then compared them with the
measured HO2 þ RO2 data (Fig. 2). In general, the field campaigns
yield higher peroxy radical concentrations than the model, which is
not surprising given that the model contains only a limited number
of the peroxy radical precursors (VOCs).