Aerosol Acidity Sensing via Polymer Degradation.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Analytical Chemistry

Background:

• Aerosol acidity influences atmospheric chemistry and multiphase reactions, impacting climate and health.
• Measuring acidity at the single-particle level is challenging, limiting understanding of fine and coarse particles.
• Current methods rely on indirect measurements or bulk modeling, not individual particle pH.

Purpose of the Study:

• To develop and validate a novel method for determining the acidity of individual submicron atmospheric aerosol particles.
• To address the analytical gap in single-particle pH measurements.
• To investigate the relationship between particle size and aerosol acidity.

Main Methods:

• Utilized the pH-sensitive polymer poly(ε-caprolactone) (PCL) to probe particle acidity.
• Deposited submicron particles (pH 0 or 6) onto PCL films and analyzed degradation using atomic force microscopy and Raman microspectroscopy.
• Quantified polymer degradation by observing holes and changes in the carbonyl stretch (1723 cm⁻¹).

Main Results:

• Observed distinct holes in PCL films exposed to pH 0, indicating polymer degradation.
• Detected a decrease in the carbonyl stretch of PCL upon exposure to acidic particles.
• Found increased polymer degradation with decreasing particle size, suggesting higher acidity in smaller aerosols.

Conclusions:

• The PCL degradation method effectively determines individual submicron particle acidity.
• Aerosol acidity increases as particle size decreases.
• This novel approach advances the understanding of aerosol impacts on climate and health by filling a key measurement gap.