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Total Non-Methane Organic Carbon

Total Non-Methane Organic Carbon. Christophe Maris, Myeong Chung, Udo Krischke, Richard Meller and Suzanne Paulson Department of Atmospheric Sciences University of California at Los Angeles.

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Total Non-Methane Organic Carbon

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  1. Total Non-Methane Organic Carbon Christophe Maris, Myeong Chung, Udo Krischke, Richard Meller and Suzanne Paulson Department of Atmospheric Sciences University of California at Los Angeles Funding Provided by• California Air Resources Board • UC Campus-Laboratory Collaboration • California Space Institute

  2. Motivation • The goal of this work is to 1. Measure total non-methane organic compounds (TNMOC), and • 2. Determine the relationship between TNMOC and the sum of the speciated volatile organic compounds (VOC’s) measured by standard techniques. • VOC’s are one of the key determinants of air quality and control strategies. • Standard measurement methods are known to detect hydrocarbons and their oxidation products incompletely.

  3. Possible Sources of Excess TNMOC compared to the Sum of Speciated VOC’s(Standard VOC Measurement) • Compounds that are lost in the inlet or column (polars, semi-volatiles). • Compounds that are obscured in the GC baseline (hydrocarbons). • Heteroatom compounds that have a reduced response in an FID.

  4. Method • Trap VOC’s from 2 ambient air samples simultaneously in a cryogenically cooled trap. Allow CO, CO2, and CH4 to pass through. • Desorb both VOC samples. Speciated VOC’s: analyze directly with DB-1 Column, GC/FID. = Standard Measurement TNMOC:oxidize CO2, analyze as methane w/ GC/FID. = True total of VOC’s 3. Compare TNMOC with the standard measurement of VOC’s.

  5. Flow Schematic

  6. TNMOC = 620 ppbC S of Speciated VOC’s = 450 ppbC

  7. Trapping Efficiency

  8. Chamber Oxidation of m-Xylene

  9. TNMOC/S of Speciated VOC’s

  10. Weekend/Weekday UCLA 2000

  11. Weekend/Weekday UCLA 2000

  12. Excess VOC’s and O3 at West LA

  13. 9/15/00 Friday

  14. UCLA Summer, All Data

  15. Weekday vs. Weekend

  16. Sunny vs. Cloudy Days

  17. UCLA Winter

  18. Excess VOC’s vs. VOC Concentration

  19. UCLA Weekday Summer 2000 R=0.5 R=0.3

  20. 9/13/00 Wednesday, 9/17/00 Sunday

  21. Conclusions • Standard VOC measurement underestimates VOC level typically by 10-60%, total can be up to 5x higher than the sum of speciated VOC’s. • Ratio of TNMOC/S of speciated VOC’s is often inversely related to the VOC and NOx concentrations. • Excess may be associated with photochemical activity, and possibly with mixing from aloft. • Excess varies strongly with location, day of week and meteorology. • Chemical identity and source of excess VOC’s is still to be determined.

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