Development and Application of a Luminol Based Nitrogen Dioxide Detector.

Abstract

An instrument for the continuous measurement of nitrogen dioxide (NO(,2)) at all atmospheric concentration ranges and conditions was developed. The detector is based on the chemiluminescent reaction between 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol) and NO(,2) in alkaline aqueous solution. Development included the optimization of the cell design and the solution composition. Sodium sulfite (Na(,2)SO(,3)) and methanol (CH(,3)OH) were added to the solution to improve sensitivity and specificity. The detector was favorably compared to two different instruments measuring NO(,2) by NO + O(,3) chemiluminescent and by a tunable diode laser absorption spectrometry system. The detector has demonstrated a detection limit of 30 parts-per-trillion by volume (ppt) and a frequency response of 0.3 Hertz. The instrument was operated for two one month periods on Bermuda. The purpose was to study air masses from the East Coast of the United States after transport over the ocean. Average daily values were 400 ppt with values as low as 100 ppt measured. Other field experiments involved monitoring of NO(,2) in ambient air in the range of 1 to 60 parts-per-billion by volume. The instrument was also used for the measurement of NO(,2) fluxes to the ground using the eddy correlation method during the Surface Layer Air Chemistry Experiment in the summer of 1983. The detector was reconfigured to a closed flow system for the measurement of the stratospheric photolysis frequency of nitrous oxide (N(,2)O). This system converts the NO, produced by the photolysis of N(,2)O in a flowing system, to NO(,2) using CrO(,3) as the oxidizing agent. Preliminary laboratory experiments indicate the system is capable of measuring N(,2)O photolysis frequencies as low as 1.7 x 10('-10) sec('-1). This detection limit is adequate for monitoring the solar photolysis of N(,2)O at all solar zenith angles at altitudes above 20 km.