Ozone Cross-Section Measurement by Gas Phase Titration.

Area of Science:

• Atmospheric Chemistry
• Metrology

Background:

• Ground-level ozone (O3) is a regulated air pollutant impacting health and materials.
• Current ozone monitoring relies on UV absorption instruments traceable to standard reference photometers.
• The accuracy of these instruments depends on the precise value of the ozone absorption cross-section at 253.65 nm.

Purpose of the Study:

• To redetermine the ozone absorption cross-section at 253.65 nm.
• To improve the accuracy of ozone measurements for air quality monitoring.
• To provide a revised, more reliable value for the ozone cross-section.

Main Methods:

• Utilized gas phase titration (GPT) measurements at the BIPM facility.
• Employed state-of-the-art flow measurement, chemiluminescence for NO, and cavity phase shift analyzer (CAPS) for NO2.
• Performed titration experiments over a 100-500 nmol/mol concentration range using diluted standards.

Main Results:

• Calculated ozone absorption cross-section values of 11.24 × 10⁻¹⁸ cm² molecule⁻¹ (±1.8% uncertainty) based on NO titration.
• Obtained a value of 11.22 × 10⁻¹⁸ cm² molecule⁻¹ (±1.4% uncertainty) based on NO2 titration.
• Reported values show excellent agreement with recent direct measurements on pure ozone.

Conclusions:

• The redetermined ozone cross-section values support revising the conventionally accepted value.
• The findings enhance the accuracy of ozone monitoring and air quality assessments.
• This work contributes to improved traceability and reliability in atmospheric measurements.