The isotopic composition of tropospheric ozone in three environments

Ground-level ozone (O-3) has been sampled from three environments: La Jolla and Pasadena, California, and White Sands Missile Range, New Mexico, using recently developed techniques for cryogenically collecting and isotopically analyzing samples of atmospheric O-3. Significant isotopic variability is observed at each location, in addition to potentially important differences between the sampling locations. The isotopic composition of O-3 is a sensitive indicator for the formation and decomposition processes which have influenced the O-3 reservoir. Thus the isotopic characterization of ground-level O-3 could provide a new source of information regarding atmospheric transformation mechanisms. To date, the measured isotopic variability in ground-level O-3 shows no correlation with O-3 or NOx mixing ratios, meteorological parameters, or time of day. However, preliminary results show a correlation between the pattern of isotopic fractionation and degree of photochemical control over the local O-3 budget at each sampling location. It should be noted that the conclusions presented are preliminary because of the relatively small data sets, particularly at the Pasadena and New Mexico locations. However, we believe that the results of this research indicate that the isotopic composition of tropospheric O-3 is variable and contains information which could be useful in the effort to understand the tropospheric O-3 budget.