Response to review 2

Abstract

Hydroxyl (OH) radical reactivity (k OH) has been measured for 18 years with different measurement techniques. In order to compare the performances of instruments deployed in the field, two campaigns were conducted performing experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich in October 2015 and April 2016. Chemical conditions were chosen either to be representative of the atmosphere or to test potential limitations of instruments. All types of instruments that are currently used for atmospheric measurements took part in one of the two campaigns. The results of these 5 campaigns demonstrate that OH reactivity can be accurately measured for a wide range of atmospherically relevant chemical conditions (e.g. water vapor, nitrogen oxides, various organic compounds) by all instruments. The precision of the measurements (limit of detection < 1 s −1 at a time resolution of 30 seconds to a few minutes) is higher for instruments directly detecting