Performance of an aircraft instrument for the measurement of NOy

Measurements of NO and NO y using a chemiluminescence technique were made on board a DC‐8 aircraft during NASA's Pacific Exploratory Mission‐West B (PEM‐West B). The gold converter to convert NO y species into NO was operated at a constant pressure using a servo‐controlled Teflon valve, which has been used for NO y measurements on board the ER‐2 aircraft. The results of laboratory tests and some flight data during PEM‐West B are presented. These experiments indicate no detectable inlet loss of HNO 3 in dry air, although some loss was observed at H 2 O mixing ratios of 1–2%. The laboratory tests also showed small variability in the NO y artifact, high conversion efficiency for NO 2 and HNO 3 , low HCN conversion efficiency, good repeatability of the measurements, and fast response. The control of the converter pressure during flight has been proven to be very advantageous in making reliable aircraft NO y measurements in the troposphere. The uncertainties of the NO and NO y PEM‐West B data, including the effects of HCN conversion and HNO 3 inlet loss, have been estimated.