Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO.sub.x in Beijing

Measurements of OH, HO.sub.2, complex RO.sub.2 (alkene- and aromatic-related RO.sub.2) and total RO.sub.2 radicals taken during the integrated Study of AIR Pollution PROcesses in Beijing (AIRPRO) campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8x107moleculecm-3, HO.sub.2 peaking at 1x109moleculecm-3 and the total RO.sub.2 concentration reaching 5.5x109moleculecm-3. OH reactivity (k(OH)) peaked at 89 s.sup.-1 during the night, with a minimum during the afternoon of â22s-1 on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv h.sup.-1) under the very low NO conditions (