Effects of filter internal reflection coefficient on light absorption measurements made using the integrating plate...

Area of Science:

• Atmospheric Science
• Optical Physics

Background:

• Nuclepore filters are commonly used in the integrating plate (IP) method for aerosol light absorption measurements.
• The internal reflectance of these filters is a critical factor influencing measurement accuracy.

Purpose of the Study:

• To investigate the optical properties of Nuclepore filter media.
• To understand how aerosol particles affect filter reflectance and its impact on absorption measurements.
• To develop a model accounting for variations in Nuclepore internal reflectance.

Main Methods:

• Examination of optical properties of Nuclepore filter media.
• Analysis of how aerosol particles alter the internal reflection coefficient.
• Development of a mathematical model for the optical system.
• Supplementary back reflectance measurements.

Main Results:

• Nuclepore filters exhibit high internal reflectance.
• Aerosol particles significantly alter the filter's internal reflection coefficient.
• The alteration varies with aerosol optical and physical properties.
• A model was developed to account for these reflectance variations.

Conclusions:

• The integrating plate (IP) method may overestimate aerosol light absorption by up to 30% due to filter reflectance changes.
• The magnitude of this inaccuracy can be estimated using the developed model and back reflectance measurements.