William C. Vicars, S.K. Bhattacharya, Joseph Erbland, and Joël Savarino

1. Measurement of the Oxygen Isotope Anomaly (∆17O) of Tropospheric Ozone Using a Nitrite-Coated Filter William C. Vicars, S.K. Bhattacharya, Joseph Erbland, and Joël Savarino Laboratoire de Glaciologie et Géophysique de l’Environnement Université Joseph Fourier / CNRS, Grenoble, France

2. The Oxygen Isotope “Anomaly” (Δ17O) of Ozone O3 tropo. δ17O = 0.52*δ18O Δ17O = δ17O - 0.52*δ18O Thiemens, 2006, Annu. Rev. Earth Planet Sci.

3. Isotope Transfer During NOX Oxidation heterogeneous Higher Δ17O Transfer XO RH Nighttime N2O5 NO2 NO3 X O3 O3 XONO2 XO NO2 HNO3 NO Lower Δ17O Transfer Daytime RO2 OH time scale: minutes hours to days

4. Δ17O(O3) in the Troposphere • Very few published observations of Δ17O for tropospheric ozone • Low [O3] (ppb level) • High [O2]/[O3] ratio • Initial studies depend on complicated experimental designs • Cryogenic trapping of O3 • Large amounts of liquid helium • Not applicable for field studies • Data may suffer from systematic errors • Low O3 collection efficiency • Interferences from atmospheric xenon Morin et al., 2007, Atmos. Chem. Phys. Krankowsky et al., 1995, Geophys. Res. Lett.

5. Collection of O3 with Nitrite (NO2-) • Has been applied in many previous studies to determine [O3] using both passive and active sampler designs • Rapid oxidation, quickly goes to completion • Specific collection and measurement of O3 • Negligible interference from other atmospheric oxidants • Yields [O3] measurements in agreement with traditional measurement techniques (UV absorbance, etc.) NO2- + O3 —› NO3- + O2 Michalski and Bhattacharya, 2009, PNAS • Terminal oxygen atom transfer • Δ17O(O3)terminal = 3/2*Δ17O(O3)bulk • Δ17O(NO3-) = 1/3*Δ17O(O3)terminal • Δ17O(NO3-) = 1/2*Δ17O(O3)bulk Koutrakis et al., 1993, Anal. Chem. Pehnec et al., 2003, B. Environ. Contam. Tox..

6. Collection of Ozone with a Nitrite-Coated Filter Filters (Whatman GF/A, 47mm) are coated with 1 mL NO2- solution and allowed to dry Prefilter for particle removal 15-20% loss of O3 to sampling apparatus • Overall collection efficiency (NO3- on filter/total throughput of O3) is 65-70% • Somewhat higher efficiencies for field collections (~ 75%) • Unexposed coated filters contribute approximately < 0.01 μmol (< 5%) 80-90% reaction yield for NO2- + O3 oxidation Teflon filter holder Flow regulated at ~ 3 L min-1

7. Isotopic Analysis Bacterial Denitrifier Method He N2 100 nmol NO3- Extracted with MQ Sulfamic Acid Treatment for NO2- Removal Neutralized with NaOH (pH = 7) Incubation (12 hours) N2O NO3- NO3-N2O NO3- Concentration Analysis (CFA) Pseudomonas Aureofaciens N2O Calibration (USGS 34 & 35) O2 N2 O2 + N2 GC MS Au, 900°C

8. Isotope Transfer Experiments Vacuum gauge ∆17O(O3)bulk N2 Pumps O2 He ∆17O(NO3-) Tesla coil Styrofoam balcony

9. Isotope Transfer during Nitrite/Ozone Oxidation Δ17O(NO3-)= 1/2*Δ17O(O3)bulk

10. Δ17O of Ambient Tropospheric Ozone Δ17O(O3)bulk = 18 - 29 ‰

11. Conclusions Advantages • The nitrite-coated filter method offers several advantages over previous techniques: • Simple technologies, can be implemented nearly anywhere (e.g., alpine and polar environments, remote ocean, stratosphere) • Not susceptible to a systematically low collection efficiency or interferences from other compounds • Provides a direct isotopic measurement of the O-atom of O3 that is transferred during oxidation reactions, rather than a bulk isotopic measurement • Due to a relatively high flow rate and low sample size requirement, samples can be collected at a high frequency allowing for an increased time resolution

12. Conclusions Limitations • Method may not be appropriate for O3 concentrations less than ~ 30 ppb at the studied flow rate • Filter blanks higher than 5-10% of NO3- formed via O3/NO2- reaction on filter • Increased sampling duration  lower time resolution • Increased flow rate  reduced ozone collection efficiency? • Large “matrix” blanks result in greater uncertainty compared to samples prepared in ultra-pure water • Increased corrections for delta values • Depends on blank/sample ratio

13. Thank You!