Intercomparison of NO, NO2, NOy, O3 and ROx measurements during the OCTA (Oxidizing Capacity of the Tropospheric Atmosphere) campaign 1993 at Izana

An informal comparison of NO, NO2, NOy, O3, and ROx measurements obtained by different instruments and techniques at Izana in 1993 during the European Oxidizing Capacity of the Tropospheric Atmosphere (OCTA) campaign was performed. For O3, two UV instruments agree within 7% (95% cl.) limited by a difference in response of 7.0%±0.2% (95% cl.) which likely was caused by O3 losses in one of the inlet lines. The NO mixing ratios obtained by two NO/O3 Chemiluminescence (CL) instruments range between 0–200 parts per trillion by volume (pptv), except for short periods influenced by traffic pollution. The response of the two CL detectors agrees within 3%±10% (95% cl.). The NOy data, ranging between 100 pptv and several ppbv in plumes, were obtained using two different gold-CO-converters and inlet designs with subsequent CL detection of NO. A systematic difference in the slope between the two data series of 1.44±0.05 (95% cl.) was likely caused by NOy, losses in the inlet line of one of the instruments. Three different NO2 data sets were obtained using Tunable Diode Laser Absorption Spectroscopy (TDLAS), a photolytic converter/CL technique (PLC/CL), and the Matrix Isolation Electron Spin Resonance (MIESR) technique. The linear slopes between the data sets of the three methods are consistent with unity at a 95% confidence level, 1.13±0.30 (TDL versus PLC/CL), 0.90±0.47 (TDL versus MIESR), and 1.04+0.34 (PLC/CL versus MIESR). ROx measurements were performed by three different chemical amplifier (CA) designs and the MIESR technique. Using 30-min averaged values between 13–65 pptv, two CA instruments agree within 25% (95% cl.) with the mean of MIESR (1.01+0.20 and 0.98±0.24, 95% cl.), while the third CA responded low (0.65±0.32, 95% cl.).