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

Laboratoire de Glaciologie et Géophysique de l’Environnement Université Joseph Fourier / CNRS, Grenoble, France

The Oxygen Isotope “Anomaly” (Δ17O) of Ozone

Thiemens, 2006, Annu. Rev. Earth Planet Sci.

O3 tropo.

δ17O = 0.52*δ18O

Δ17O = δ17O - 0.52*δ18O

Isotope Transfer During NOX Oxidation

NO

O3

X

XO

NO2

RO2

XOXONO2

NO3

N2O5

O3

NO2

RH

OH

Nighttime

Daytime

HNO3

Lower Δ17O Transfer

Higher Δ17O Transfer

time scale: minutes hours to days

heterogeneous

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.

Collection of O3 with Nitrite (NO2-)

Michalski and Bhattacharya, 2009, PNAS

Koutrakis et al., 1993, Anal. Chem.Pehnec et al., 2003, B. Environ. Contam. Tox..

NONO22-- + O + O33 —› NO —› NO33

-- + O + O22NONO22-- + O + O33 —› NO —› NO33

-- + O + O22

• 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 O3一 Negligible interference from

other atmospheric oxidants• Yields [O3] measurements in

agreement with traditional measurement techniques (UV absorbance, etc.)

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

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

Teflon filter holder

Flow regulated at ~ 3 L min-1

15-20% loss of O3 to sampling apparatus

80-90% reaction yield for NO2

- + O3 oxidation80-90% reaction yield for NO2

- + O3 oxidation

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%)

Extracted with MQ

100 nmol NO3-

Incubation(12 hours)

He

NO3- N2O

Au, 900°C

O2 + N2O2 N2

MS

Calibration (USGS 34 & 35)PseudomonasAureofaciens

GC

Sulfamic Acid Treatment

for NO2- Removal

N2

Neutralizedwith NaOH

(pH = 7)

Bacterial Denitrifier Method

NO3-

N2O

N2ONO3

- Concentration Analysis (CFA)

Isotopic AnalysisIsotopic Analysis

Isotope Transfer Experiments

∆∆1717O(OO(O33))bulkbulk

Vacuum gauge

PumpsTesla coil

∆∆1717O(NOO(NO33--))

Styrofoam balcony

Isotope Transfer during Nitrite/Ozone Oxidation

Δ17O(NO3-) = 1/2*Δ17O(O3)bulk

Δ17O of Ambient Tropospheric Ozone

Δ17O(O3)bulk = 18 - 29 ‰

• 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

ConclusionsConclusions

Advantages

• 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

ConclusionsConclusions

Limitations

Thank You!