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Measurement of NO y During SCOS97-NARSTO

This study focuses on the measurement of NOy (Reactive Oxidized Nitrogen) during the SCOS97-NARSTO project. It covers converter-based interferences, nitric acid measurement, typical data, importance of NOy, definitions, and measurement techniques used, highlighting potential interferences and the need for quality control. The research concludes with recommendations to address biases and minimize interferences in NOy measurement.

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Measurement of NO y During SCOS97-NARSTO

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  1. Measurement of NOy During SCOS97-NARSTO Dennis R. Fitz University of California, Riverside College of Engineering Center for Environmental Research and Technology

  2. ORGANIZATION • NOy BACKGROUND • CONVERTER-BASED INTERFERENCES • NITRIC ACID • TYPICAL DATA • CONCLUSIONS

  3. 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

  4. 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

  5. (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

  6. INTERFERENCES • Chemiluminescent Analyzer • Converter • Both have become more noticeable with commercial analyzers as they have become more sensitive

  7. 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

  8. INTERFERENCES - HEATED CONVERTERS • Variable Efficiency for Nitrogenous Species • Conversion of Ammonia and Amines • Conversion of Cyanides

  9. 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

  10. INTERFERENCE TEST SYSTEM

  11. AMMONIA COVERTER EFFICIENCY FOR THERMOENVIRONMENTAL MOLY CONVERTER56 ppb Ammonia - Dry

  12. 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

  13. NO Analyzer NOy Converter 3- Way Solenoid Valve External Converter Housing NaCl Coated Filter NO Detector NOy Converter NITRIC ACID MEASUREMENT

  14. TYPICAL RESPONSE LAG DUE TO MEMORY EFFECT To Zero Air 1005

  15. Typical Measurements-Azusa

  16. Typical Results-Azusa

  17. HNO3 Comparison vs TDLAS

  18. Typical Results- Simi Valley

  19. SMOG CHAMBER NOy -NA

  20. NOy RESPONSE TO FILTERED AIR WITH NITRIC ACID REMOVED

  21. 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)

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