Development of a new LOPAP instrument for the detection of O3 in the atmosphere

A simple O3-LOPAP (Long Path Absorption Photometer) instrument for the selective detection of O3 in the atmosphere is presented, which is mainly intended to be used as an extension of a recently developed NO2-LOPAP. O3 is sampled in a stripping coil by a selective chemical reaction with the highly absorbing Indigo dye. The reduction of the optical absorption of the dye is detected in a liquid core waveguide. The instrument has a detection limit of 0.4 ppbv, an accuracy of 10%, a precision of 2% for 6 min time resolution and allows the absolute quantification of O3 according to Lambert–Beerʹs law. Interferences towards nitrogen oxides (NO and NO2), N2O5, H2O2 and several VOCs were quantified in the laboratory and found to be negligible for atmospheric conditions. The new instrument was successfully validated against a commercial UV-absorption instrument during an urban field campaign and against the FTIR technique in a smog chamber under complex photosmog conditions. For the UV-absorption instrument significant positive interferences towards aromatic species were observed in the smog chamber.