INTERCOMPARISON OF NO, NO2, NOY, O-3, AND ROX MEASUREMENTS DURING THEOXIDIZING CAPACITY OF THE TROPOSPHERIC ATMOSPHERE (OCTA) CAMPAIGN 1993 AT IZANA

An informal comparison of NO, NO2, NOy, O-3, and ROx measurements obta ined by different instruments and techniques at Izana in 1993 during t he European Oxidizing Capacity bf the Tropospheric Atmosphere (OCTA) c ampaign was performed. For O-3, 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 O-3 losses in one of the inlet lines. The N O mixing ratios obtained by two NO/O-3 Chemiluminescence (CL) instrume nts range between 0-200 parts per trillion by volume (pptv), except fo r short periods influenced by traffic pollution.. The response of the two CL detectors agrees within 3%+/-10% (95% cl.). The NOy data, rangi ng between 100 pptv and several ppbv in plumes, were obtained using tw o different gold-CO-converters and inlet designs with subsequent CL de tection of NO. A systematic difference in the slope between the two da ta 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 set s were obtained using Tunable Diode Laser Absorption Spectroscopy (TDL AS), a photolytic converter/CL technique (PLC/CL), and the Matrix Isol ation Electron Spin Resonance (MIESR) technique. The linear slopes bet ween 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 (T DL versus MIESR), and 1.04+/-0.34 (PLC/CL versus MIESR). RO, measureme nts were performed by three different chemical amplifier (CA) designs and the MIESR technique. Using 30-min averaged values between 13-65 pp tv, two CA instruments agree within 25% (95% cl.) with the mean of MIE SR (1.01+/-0.20 and 0.98+/-0.24, 95% cl.), while the third CA responde d low (0.65+/-0.32, 95% cl.).