NOX

The ARM ground-based NO/NO₂/NO_y (Nitrogen Oxides) Monitor is based on detecting chemiluminescence resulting from the highly specific reaction of ambient NO reacting with reagent ozone.  NO₂ is converted to NO using a high-power LED  photolysis cell which has a 75-80% conversion efficiency.  The NO/NO₂ channel alternately measures NO and NO + NO₂ measured with a modified commercial NO instrument.  A second dedicated NO instrument measures total NO_y following conversion to NO in a heated molybdenum converter with ~99% conversion efficiency.  A thermally controlled inlet box is external to the AOS at a sampling height of 10 m and contains mass flow controllers and converters to eliminate losses in the tubing.   The instrument system includes automatic calibration capabilities at the sampling inlet for NO and gas-phase titration of NO to NO₂ to measure basic sensitivity and conversion efficiency.  The molybdenum converter is also tested against HNO₃ in the laboratory.

The instrument system includes an internal computer that controls multiple switching cycles, real-time display, and sends a complete set of raw data to the site data system.

• Nitrogen oxides