Research Projects

Project at a Glance

Project Status: complete

Title: The relationship between total non-methane organic carbon and the sum of speciated hydrocarbons and carbonyls measured by standard GC/FID: validation and refinement of a new instrument, and measurements in the South Coast Air Basin.

Principal Investigator / Author(s): Paulson, Suzanne

Contractor: UC Los Angeles

Contract Number: 98-323


Research Program Area: Atmospheric Processes

Topic Areas: Field Studies


Abstract:

Here we describe development of a new instrument to measure the airborne total non-methane organic carbon concentration (TNMOC), and the ratio of this value to the sum of speciated volatile organic carbon (VOCís) measured by standard gas chromatography. The approach is to make a measurement that minimizes sample contact, cryo-trapping whole air samples with minimal trapping of carbon dioxide, carbon monoxide and methane. Samples are processed by an oxidation catalyst to generate carbon dioxide that is measured as TNMOC. Simultaneously, a standard speciated VOCís measurement is made with the same instrument. The ratio of the TNMOC and speciated VOCís measurements provides the ďexcess VOCísĒ, or that not detected by routine monitoring techniques. Measurements of ambient air were made in West Los Angeles, Burbank and Azusa. Fresh pollution sources including gasoline vapor and diesel exhaust were tested as well. These sources are, not surprisingly, measured well by the standard analysis approach, and had 5-20% ďexcessĒ VOCís. The Burbank site, which is surrounded by freeways and light industrial sources had only 10 % excess VOCís, as did UCLA during winter when there is minimal photochemistry. In contrast, between 25 and 45% of the VOCís were unmeasured by the standard technique at the UCLA and Azusa sites during summer. The dominant source of the unmeasured VOCís appears to be air that has been aged for more than 12 hours, possibly for a day or more.


 

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