Stable Carbon Isotope Ratio Measurements: A New Tool to Understand Atmospheric Processing of Volatile Organic Compounds

Abstract

Measurements of stable isotope ratios have been extremely valuable to better understand the atmospheric cycles of a number of important trace gases, such as ozone, carbon monoxide and — dioxide, nitrous oxide, methane and hydrogen (c.f. Lowe et al., 1994; Conny and Currie, 1996; Conny et al., 1997; Manning et al., 1997; Brenninkmeijer and Rockrnann, 1997; Manning, 1999; Lowe et al., 1999). Due to experimental limitations, applications of stable isotope ratio measurements for gas phase components generally have been limited to studies of compounds that are present in the atmosphere at levels of at least several ten ppb. Only recently it has been demonstrated that the stable carbon isotope ratio measurements of volatile organic compounds (VOC) in the atmosphere are possible at sub-ppb levels (Rudolph et al., 1997). Traditionally, applications of stable isotope ratio measurements focus on constraining atmospheric trace gas budgets and source apportionment. However, it has been shown that stable carbon isotope ratios of atmospheric VOC can also be used to determine the extent of chemical processing (“photochemical age”) of the studied compound since its emission into the atmosphere (Rudolph and Czuba, 1999).