Dual-inlet chemical amplifier for atmospheric peroxy radical measurements

The state-of-the-art of peroxy radical measurements using the technique of chemical amplification has matured in recent years. The NCAR chemical amplifier has been improved over previous versions by employing a dual-inlet system that allows more rapid switching between measurement and background modes. Further improvement is realized by the use of two NO2 detectors. The dual-inlet chemical amplifier (DICHAMP) employs two identical glass inlet reactor-NO2 detector combinations, one of which is operated in the background, while the other operates in the radical measurement mode. This instrument is less sensitive to fluctuations in ambient ozone than the single-channel version because of the continuous monitoring of the background and background plus radical signals. The single-inlet, dual-inlet with single-detector, and DICHAMP instruments are compared through theoretical calculations of the effect of noise at a given frequency and amplitude on retrieved radical levels, Laboratory experiments were conducted to support the theoretical results. Ambient radical concentrations were determined using these configurations to evaluate the performance under actual measurement conditions.