Isotopic (14C) and Chemical Composition of Atmospheric Volatile Organic Compound Fractions-Precursors to Ozone Formation.

摘要

Atmospheric volatile organic compounds (VOCs) are an important factor in the production of ozone near ground level (3). Many hydrocarbons originate from auto exhaust. However, a number of VOCs, e.g., isoprene, are known to be natural in origin. To develop reliable models for understanding how ozone levels might be controlled, it has been recognized that a key variable is the fractional amount of fossil vs non-fossil (biogenic, uncontrollable) VOCs (1). These two source categories are uniquely discriminated from each other based on the 14C abundance of VOC fractions. Combining isotopic measurements with chemical information will yield greater confidence in source estimates. Over the last 8 years, NIST, OGI and the U.S. EPA have explored sampling methods and analytical procedures to collect enough carbon from atmospheric non-methane VOC fractions to measure the 14C composition (4, 9). In doing so, this work also provided an opportunity to enhance the sensitivity of GC-FID and GC-MS for chemical identification and quantification. This paper will briefly describe the methods studied and present preliminary 14C and chemical results from Azusa, CA, Houston, TX, and Nashville, TN, USA.