Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles

Area of Science:

• Atmospheric Science
• Optical Physics
• Aerosol Science

Background:

• Soot particles, common atmospheric aerosols, are often coated with various substances.
• The optical properties of these coated particles significantly influence Earth's radiative balance and climate.
• Understanding the impact of coating materials on soot optical properties is vital for accurate climate modeling.

Purpose of the Study:

• To investigate the influence of different coating materials (toluene-based and sulfate) on the optical properties of soot aggregates.
• To determine the sensitivity of extinction-to-backscatter ratio (lidar ratio) and depolarization ratio to coating composition.
• To assess the Ångström exponents for different coating materials across multiple wavelengths.

Main Methods:

• Computation of optical properties for 58 differently sized coated soot aggregates.
• Calculation of extinction-to-backscatter ratio and depolarization ratio at 355 nm, 532 nm, and 1064 nm.
• Determination of Ångström exponents between 355-532 nm and 532-1064 nm.

Main Results:

• The extinction-to-backscatter ratio clearly distinguishes between toluene and sulfate coatings at all three wavelengths.
• The depolarization ratio effectively differentiates the coating materials at 355 nm and 532 nm.
• Ångström exponents also show variations indicative of coating material differences.

Conclusions:

• Optical properties, specifically lidar ratio and depolarization ratio, serve as reliable indicators for identifying coating materials on soot particles.
• These findings enhance the ability to characterize atmospheric aerosols and improve climate models.
• The study highlights the importance of considering coating composition in aerosol optical studies.