Quantitative constraints on the 17O-excess (Δ17O) signature of surface ozone: Ambient measurements from 50°N to 50°S using the nitrite-coated filter technique

The unique and distinctive O-17-excess (Delta O-17) of ozone (O-3) provides a conservative tracer for oxidative processes in both modern and paleo-atmospheres and has acted as the primary driver of theoretical and experimental research into non-mass-dependent fractionation (NMDF) for over three decades. However, due to the inherent complexity of extracting O-3 from ambient air, the existing observational dataset for tropospheric O-3 isotopic composition remains quite small. Recent analytical developments have provided a robust and reliable means for determining Delta O-17(O-3)(trans.), the transferrable Delta O-17 signature of ozone in the troposphere (Vicars et al., 2012). We have employed this new methodology in a systematic investigation of the spatial and seasonal features of Delta O-17(O-3)(trans.) in two separate field campaigns: a weekly sampling effort at our laboratory in Grenoble, France (45 degrees N) throughout 2012 (n = 47) and a four-week campaign onboard the Research Vessel (R/V) Polarstern along a latitudinal transect from 50 degrees S to 50 degrees N in the Atlantic Ocean (n = 30). The bulk O-17-excess of ozone, denoted Delta O-17(O-3)(bulk), exhibited mean (+/- 1 sigma) values of 26.2 +/- 1.3 parts per thousand (Delta O-17(O-3)(trans.) = 39.3 +/- 2.0 parts per thousand) and 25.9 +/- 1.1 parts per thousand (Delta O-17(O-3)(trans.) = 38.8 +/- 1.6 parts per thousand) for the Grenoble and R/V Polarstern collections, respectively. This range of values is in excellent quantitative agreement with the two previous studies of ozone triple-isotope composition, which have yielded mean (+/- 1 sigma) Delta O-17(O-3)(bulk) values of 25.4 +/- 9.0 parts per thousand (n = 89). However, the magnitude of variability detected in the present study is much smaller than that formerly reported. In fact, the standard deviation of Delta O-17(O-3)(bulk) in each new dataset is lower than the uncertainty previously estimated for the filter technique (+/- 1.7 parts per thousand), indicating a low level of natural spatial and temporal variation in the O-17-excess of surface ozone. For instance, no clear temporal pattern in Delta O-17(O-3) is evident in the annual record from Grenoble despite dramatic seasonal variations in ozone and atmospheric reactive nitrogen (NOx = NO + NO2) concentrations. However, a small but statistically significant difference is distinguishable in the R/V Polarstern record when comparing samples collected in the Southern and Northern Hemispheres, which possessed average Delta O-17(O-3)(bulk) values of 25.2 +/- 1.0 parts per thousand and 26.5 +/- 0.7 parts per thousand, respectively. The implications of these results are discussed in the context of the tropospheric ozone budget and the use of oxygen isotope ratios of secondary atmospheric species to derive information regarding oxidation pathways from modern and paleo-atmospheres. (C) 2014 Elsevier Ltd. All rights reserved.