17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

Area of Science:

• Atmospheric Chemistry
• Isotope Geochemistry

Background:

• Ozone's unique 17O excess (Δ17O) can trace atmospheric oxidation.
• Quantitative understanding of oxygen transfer in NO2 + O3 reactions is lacking.
• This reaction is crucial for nocturnal nitrate production.

Purpose of the Study:

• Investigate Δ17O transfer from ozone to nitrate radical (NO3) in the gas-phase NO2 + O3 reaction.
• Determine the Δ17O transfer function for this specific reaction.
• Understand intramolecular oxygen isotope distribution in ozone.

Main Methods:

• Laboratory experiments to study the gas-phase NO2 + O3 reaction.
• Isotope ratio mass spectrometry to measure isotopic composition (δ17O, δ18O) of ozone and oxygen gas.
• Analysis of Δ17O transfer and intramolecular oxygen distribution.

Main Results:

• Determined the Δ17O transfer function for the NO2 + O3 reaction: Δ17O(O3*) = (1.23 ± 0.19) × Δ17O(O3)(bulk) + (9.02 ± 0.99).
• Found that excess 17O enrichment in ozone predominantly resides on terminal oxygen atoms.
• Quantified the isotopic signal transfer during this key atmospheric reaction.

Conclusions:

• Provides a quantitative understanding of Δ17O transfer in the NO2 + O3 reaction.
• Enables more accurate interpretation of high Δ17O values in atmospheric nitrate.
• Improves understanding of atmospheric reactive nitrogen cycling and ozone's role.