Citation:

Klouda, G., J. Norris, L. Currie, G. Rhoderick, R. Sams, W. Dorko, C. Lewis, W.A. Lonneman, R. Seila, AND R. Stevens. METHOD FOR SEPARATING VOLATILE ORGANIC CARBON FROM 0.1 M3 OF AIR TO IDENTIFY SOURCES OF OZONE PRECURSORS VIA ISOTOPE (14C) MEASUREMENTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-93/222 (NTIS PB93236511), 1993.

Description:

Atmospheric non-methane volatile organic compounds (VOCS) are known to play an important role in urban ozone formation during the summer. o respond to the need for a direct measure of VOC source contributions from biogenic (14C/12C=10-12) and fossil fuel (14C/12C=O) emissions, a system and protocol are being developed to separate the total VOC fraction, which would amount to micrograms of carbon, from 0.1 M3 of ambient air for accelerator mass spectrometry (AMS) 14C. he gas separation system developed at NIST allows for the simultaneous separation of low vapor pressure (LVP) VOCs and H20, high vapor pressure (HVP) VOCs and CO2, CO and CH4 through sequential cryogenic separation and selective oxidation techniques. reliminary results of this system and procedure for isolating these fractions show a LVP-VOC blank of 2 +/- 1 ug C, which represents the effect of the separation system plus CO2 cross-contamination. ydrocarbons having vapor pressures greater than n-decane are not retained at a level of more than a few percent in the LVP-VOC fraction. n upper limit of the HVP-VOC blank has been estimated at 7 +/- 8 ug C. The recovery of C5-C8 hydrocarbons in the combined HVP-VOC and CO2 fraction ranges from 27% to 78%. ower recoveries were observed for these same compounds in a hydrocarbon standard having 2 orders of magnitude less CO2 than ambient concentrations. t is expected that yields for this VOC fraction will improve substantially by substituting the existing cryo-trap with a Russian Doll trap.

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