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Measurement of NO y During SCOS97-NARSTO. Dennis R. Fitz University of California, Riverside College of Engineering Center for Environmental Research and Technology. ORGANIZATION. NO y BACKGROUND CONVERTER-BASED INTERFERENCES NITRIC ACID TYPICAL DATA CONCLUSIONS. NO y IMPORTANCE.
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Measurement of NOy During SCOS97-NARSTO Dennis R. Fitz University of California, Riverside College of Engineering Center for Environmental Research and Technology
ORGANIZATION • NOy BACKGROUND • CONVERTER-BASED INTERFERENCES • NITRIC ACID • TYPICAL DATA • CONCLUSIONS
NOy IMPORTANCE • Mass Balance • Quality control • Missing species • Estimate Nitric Acid by Difference • Sum of other species • Scrub nitric acid and use a second converter and analyzer channel
DEFINITIONS • NOy = Reactive Oxidized Nitrogen (N2O not included) • NOy = NO + NO2 +HNO3 + PAcN + HONO+ 2N2O5 + HO2NO2 + Organic Nitrates + NO3 + NO3- • (NOy)i = Catalytically Reduced NOy • NOx = NO + NO2 • NOz = NOy - NOx
(NOy)i MEASUREMENT • Chemiluminescent NO Analyzer • (NOy)i Converter to NO Located Outside Without an Inlet Filter (to reduce HNO3 losses) • Heated Molybdenum (300°-350°C) • Heated Gold (400°C) + CO (or H2) • Heated Vitreous Carbon (350°C) • Ferrous Sulfate
INTERFERENCES • Chemiluminescent Analyzer • Converter • Both have become more noticeable with commercial analyzers as they have become more sensitive
INTERFERENCES - ANALYZER • Water Vapor- Quenching • Zero (sub ppb) • Span (can be 10 %) • Methods to Minimize • Zero and/or Calibrate with Ambient Air Scrubbed of NOy • Method of Standard Addition
INTERFERENCES - HEATED CONVERTERS • Variable Efficiency for Nitrogenous Species • Conversion of Ammonia and Amines • Conversion of Cyanides
MOLYBDENUM CONVERTER CHARACTERISTICS • Ammonia Conversion • “Memory Effect” (High NOy or Hydrocarbon Concentrations) • Long stabilization period • Elevated “zero” response • Compound Selective Degradation • Lowered Efficiencies at Atmospheric Pressure
AMMONIA COVERTER EFFICIENCY FOR THERMOENVIRONMENTAL MOLY CONVERTER56 ppb Ammonia - Dry
NITRIC ACID MEASUREMENT • Use dual converters and scrub nitric acid (NA) using a denuder from the inlet of one to obtain NA by difference • Problems • Difference between large numbers • Converter efficiencies must be exactly the same for all NOy species and interferences • NOy memory effect greater than NOy -NA
NO Analyzer NOy Converter 3- Way Solenoid Valve External Converter Housing NaCl Coated Filter NO Detector NOy Converter NITRIC ACID MEASUREMENT
TYPICAL RESPONSE LAG DUE TO MEMORY EFFECT To Zero Air 1005
CONCLUSIONS • Present converters have significant biases and interferences • Frequent (hourly?) zero checks are needed to assess memory effect • Routine converter efficiency checks for major NOy species and ammonia are needed • Acid coated denuders should be tried to remove ammonia (but let all NA pass)