Characterization of fine mode atmospheric aerosols by Raman microscopy and diffuse reflectance FTIR

Area of Science:

• Atmospheric Chemistry
• Spectroscopy
• Environmental Science

Background:

• Tropospheric aerosols significantly impact climate and air quality.
• Characterizing fine mode aerosols (<1 μm) is crucial for understanding their atmospheric behavior.
• Previous methods lacked particle-level resolution for complex aerosol mixtures.

Purpose of the Study:

• To characterize the composition and mixing state of fine mode tropospheric aerosols.
• To utilize Raman microscopy and FTIR spectroscopy for detailed aerosol analysis.
• To identify specific organic carbon species within the aerosols.

Main Methods:

• Combined Raman microscopy and diffuse reflectance Fourier transform infrared spectroscopy (FTIR).
• Employed peak fitting on Raman spectra to identify carbonaceous and organic bands.
• Utilized spectral mapping for particle-level composition and mixing state determination.

Main Results:

• Identified overlapping Raman bands indicative of carbon soot and large molecular organic carbon species.
• Established Raman spectral features (D band fwhm, D3/G band ratio) as measures of organic carbon content.
• Determined fine aerosols are predominantly internally mixed: carbon soot cores coated with organic matter.
• FTIR analysis identified polycarboxylates and polysaccharide-like species (humic-like substances - HULIS) as major organic components.

Conclusions:

• Raman microscopy and FTIR provide powerful, complementary tools for fine aerosol characterization.
• Fine tropospheric aerosols are complex, internally mixed structures.
• Humic-like substances (HULIS) are significant organic components of these aerosols, influencing their properties.