Calorimetric measurement of optical absorption

Area of Science:

• Atmospheric Science
• Optical Physics
• Aerosol Science

Background:

• Accurate measurement of aerosol optical properties is vital for climate modeling.
• Understanding shortwave radiation absorption by airborne particles influences atmospheric heating and radiative transfer.
• Existing methods for measuring particle absorption coefficients have limitations.

Purpose of the Study:

• To develop and validate a novel method for determining the mean shortwave volume absorption coefficient of airborne particles.
• To compare the performance of the new method with existing calorimetric and photometric techniques.
• To assess the detection limits and practical applicability of the developed technique.

Main Methods:

• Airborne particles are introduced into a sealed chamber and irradiated with broadband shortwave radiation.
• The pressure change over time within the chamber is measured to calculate the volume absorption coefficient.
• The method was calibrated using water vapor to ensure accuracy.

Main Results:

• The mean shortwave volume absorption coefficient was successfully calculated from pressure changes.
• A detection limit of +/-2 x 10(-6)/m was achieved for the volume absorption coefficient.
• Excellent agreement was observed between the new calorimetric method and a novel photometric absorption measurement.

Conclusions:

• The developed method provides a reliable way to measure airborne particle shortwave absorption.
• The technique offers a valuable alternative for aerosol optical property characterization.
• Further discussion on the advantages and disadvantages of calorimetric and photometric methods is presented.