Effect of soot microstructure on its ozonization reactivity.

Area of Science:

• Chemical kinetics
• Atmospheric chemistry
• Materials science

Background:

• Ozone (O3) uptake by soot particles is crucial for atmospheric chemistry, but large uncertainties exist in measured coefficients.
• Soot properties, including source and microstructure, are suspected to influence O3 reactivity.

Purpose of the Study:

• To investigate how soot microstructure, controlled by fuel/oxygen ratios during combustion, affects its reactivity towards ozone.
• To identify the specific carbon structures within soot responsible for ozone uptake.

Main Methods:

• Controlled combustion of n-hexane to produce soot samples with varying microstructures.
• In situ Raman spectroscopy to analyze soot structure and identify reactive components.
• Kinetic studies to quantify ozone uptake coefficients on different soot types.

Main Results:

• Fuel/oxygen ratio significantly altered soot particle diameter and micro-chemical structure.
• Fuel-lean flame soot exhibited lower structural uniformity and higher disordered carbon content (D1, D2, D3 bands) compared to fuel-rich soot.
• Disordered carbon, particularly at surface graphene layers, was identified as the primary reactive site for ozone uptake.
• Reactivity of disordered carbon in fuel-rich soot was higher than in fuel-lean soot.

Conclusions:

• Soot microstructure, dictated by combustion conditions, is a critical factor controlling ozone uptake.
• Disordered carbon content and distribution determine soot's reactivity towards ozone.
• Understanding soot structure-ozone interactions is essential for accurate atmospheric modeling.