Measurement of the 17O-excess (?17O) of tropospheric ozone using a nitrite-coated filter

RATIONALE: The O-17-excess (Delta O-17) of tropospheric ozone (O3) serves as a useful marker in studies of atmospheric oxidation pathways; however, due to the complexity and expense of currently available analytical techniques, no systematic sampling campaign has yet been undertaken and natural variations in.O-17(O3) are therefore not well constrained. METHODS: The nitrite-coated filter method is a new technique for O3 isotope analysis that employs the aqueous phase NO2 -+ O3 ! NO3 -+ O2 reaction to obtain quantitative information on O3 via the oxygen atom transfer to nitrate (NO3 -). The triple-oxygen isotope analysis of the NO3 -produced during this reaction, achieved in this study using the bacterial denitrifier method followed by isotope-ratio mass spectrometry (IRMS), directly yields the.O-17 value transferred from O3. This isotope transfer process was investigated in a series of vacuum-line experiments, which were conducted by exposing coated filters to O3 of various known.O-17 values and then determining the isotopic composition of the NO3 -produced on the filter. RESULTS: The isotope transfer experiments revealed a strong linear correlation between the.O-17 of the O3 produced and that of the oxygen atom transferred to NO3 -, with a slope of 1.55 for samples with bulk.O-17(O3) values in the atmospheric range (20-40%). This finding is in agreement with theoretical postulates that place the O-17-excess on only the terminal oxygen atoms of ozone. Ambient measurements yield average.O-17(O3) bulk values in agreement with previous studies (22.9 +/- 1.9%). CONCLUSIONS: The nitrite-coated filter technique is a sufficiently robust, field-deployable method for the determination of the triple-oxygen isotopic composition of tropospheric O3. Further ambient measurements will undoubtedly lead to an improved quantitative view of natural.O-17(O3) variation and transfer in the atmosphere. Copyright c 2012 John Wiley & Sons, Ltd.