Chemical ionization mass spectrometer technique for the measurement of HNO sub(3) in air traffic corridors in the upper troposphere during the SONEX campaign

A chemical ionization mass spectrometer (CIMS) was used for rapid detection of HNO sub(3) in air traffic corridors, primarily over the North Atlantic region, during the NASA Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) campaign in the fall of 1997. The sensitivity of the CIMS instrument approaches 1 ion count per second for each 10 super(6) molecules cm super(-) super(3) , under ideal conditions. During the SONEX mission the precision of the experiment was considerably lower due to inlet fluctuations. Ten-second integration periods were used to obtain a precision of typically 10 parts per trillion by volume. A description is given of the instrument and the technique, including inflight calibration using a permeation tube. Comparisons are made with NO sub(y) data and with the University of New Hampshire HNO sub(3) data obtained with a mist chamber method.