Research Program Area: Atmospheric Processes
ARB Project No. 95-335, entitled, "Total Non-Methane Organic Carbon: Development and Validation of a New Instrument and Measurements of Total Non- Methane Organic Carbon and C2-C10 Hydrocarbons in the South Coast Air Basin," covering the funding period from 8/96-8/98, resulted in an instrument that was successfully deployed at Pico Rivera and Azusa SCAQMD stations to measure total non-methane organic carbon (TNMOC) and the speciated VOC's. The latter field campaign was part of SCOS-NARSTO-97. At Azusa during September and early October, 1997 the TNMOC loading was an average of 30% greater than the sum of the speciated VOCs measured by standard GC/FID (TNMOC/∑ speciated VOC's ratio averaged 1.3 ± 0.3.) This ratio did not correlate with time of day or photochemical processing, but the air reaching the Azusa site was abnormally clean during this period; for example 95% of corresponding O3 concentrations were < 60 ppb. The nature (and reactivity) of the 30% difference between the TNMOC and the ∑ Speciated VOC's is still to be determined. A small fraction of the difference (c. 10%) is due to light oxygenates, ethanol, methanol and acetaldehyde. The primary cause of the variability appears to be short term fluctuations in organic concentrations in the air reaching the Azusa station. Aiming to rectify this situation, the instrument has been fitted with parallel samplers that acquire simultaneous TNMOC and speciated VOC samples. Future field measurements will be made with the dual sampler.
The campaign at Pico Rivera showed that the TNMOC instrument was in excellent agreement with the co-located South Coast Air Quality Management District (SCAQMD) instrument. Experiments carried out in conjunction with SCAQMD staff scientists revealed the source of the anomalous high levels of heavy hydrocarbons that had been observed at Pico Rivera for many years-contamination from room air that escaped through the roof and was entrained into the sample inlet. The instrument was tested and validated with the light oxygenates formaldehyde, acetaldehyde, acetone, methanol and ethanol as well as heavy aromatics and exhibited 100% trapping and conversion in all cases. The instrument does not appear to be affected by water. Preliminary results indicate that the analyzer detects > 95% of carbon in smog chamber hydrocarbon oxidation experiments. Finally, a collection of Fill response factors for light oxygenates has been derived.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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