A portable high-resolution polar nephelometer for measurement of the angular scattering properties of atmospheric aerosol: Design and validation

Abstract

The light-scattering properties of atmospheric aerosol particles are important for understanding their effects on Earth's climate, remote sensing studies of particulate matter, and visibility studies. However, aerosol optical properties are relatively poorly understood and have been identified as one of the largest uncertainties in our understanding of anthropogenic effects on climate. Direct in situ and laboratory studies of aerosol light-scattering may help reduce these uncertainties and improve remote sensing studies. A field-deployable, high angular resolution polar nephelometer has been developed for the measurement of the scattering properties of aerosol particles. The instrument utilizes an elliptical mirror, laser, and charge-coupled device camera to measure the aerosol angular scattering intensity (phase function) and degree of linear polarization (polarization ratio) across an angle range of 20°-155° at a resolution as high as 0.31°-0.59° per pixel. The instrument design was validated by laboratory measurements of the scattering properties of polystyrene latex (PSL) microspheres at a wavelength of 532 nm and comparison with Lorenz-Mie theory. The instrument accurately measured the predicted phase function and linear polarization for four sizes of monodisperse PSL with diameters ranging from 300 to 750 nm, except for very narrow features predicted by the theory. The instrument offers high angular resolution and the capability to measure multiple angles simultaneously. Advantages and disadvantages of the technique are discussed. © 2013 American Association for Aerosol Research.