Intercomparison of NO3 radical detection instruments in the atmosphere simulation chamber SAPHIR

The detection of atmospheric NO3 radicals is still challenging owing to its low mixing ratios ( 1 to 300 pptv) in the troposphere. While long-path differential optical ab- sorption spectroscopy (DOAS) has been a well-established NO3 detection approach for over 25 yr, newly sensitive tech- niques have been developed in the past decade. This pub- lication outlines the results of the first comprehensive in- tercomparison of seven instruments developed for the spec- troscopic detection of tropospheric NO3. Four instruments were based on cavity ring-down spectroscopy (CRDS), two utilised open-path cavity-enhanced absorption spectroscopy (CEAS), and one applied "classical" long-path DOAS. The intercomparison campaign "NO3Comp" was held at the at- mosphere simulation chamber SAPHIR in J¨ ulich (Germany)