1. Measurement of NO y During SCOS97-NARSTO Dennis R. Fitz University of California, Riverside College of Engineering Center for Environmental Research and Technology

2. ORGANIZATION NO y BACKGROUND CONVERTER-BASED INTERFERENCES NITRIC ACID TYPICAL DATA CONCLUSIONS

3. NO y 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 NO y = Reactive Oxidized Nitrogen (N 2 O not included) NO y = NO + NO 2 +HNO 3 + PAcN + HONO+ 2N 2 O 5 + HO 2 NO 2 + Organic Nitrates + NO 3 + NO 3 - (NO y ) i = Catalytically Reduced NO y NO x = NO + NO 2 NO z = NO y - NO x

5. (NO y ) i MEASUREMENT Chemiluminescent NO Analyzer (NO y ) i Converter to NO Located Outside Without an Inlet Filter (to reduce HNO 3 losses) –Heated Molybdenum (300°-350°C) –Heated Gold (400°C) + CO (or H 2 ) –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 NO y –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 NO y 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 CONVERTER 56 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 NO y species and interferences –NO y memory effect greater than NO y -NA

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

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

15. Typical Measurements-Azusa

16. Typical Results-Azusa

17. HNO 3 Comparison vs TDLAS

18. Typical Results- Simi Valley

19. SMOG CHAMBER NO y -NA

20. NO y 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 NO y species and ammonia are needed Acid coated denuders should be tried to remove ammonia (but let all NA pass)