william c. vicars, s.k. bhattacharya, joseph erbland, and joël savarino
DESCRIPTION
Measurement of the Oxygen Isotope Anomaly (∆ 17 O) 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. - PowerPoint PPT PresentationTRANSCRIPT
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!