Physico-chemical characterization of individual Antarctic particles: Implications to aerosol optics

Abstract Aerosols affect the Earth's radiation budget by interacting with the incoming solar radiation. The physico-chemical properties, particularly morphological parameters (Aspect Ratio, AR and Circulatory Factor, CIR) and composition at individual particle level are important inputs to the optical model for assessing the optical sensitivity towards said properties. The observation of these properties is limited over Antarctica which has been studied in detail in the present work. The PM 5 particles (particulate matter with aerodynamic diameter less than 5  μm) over Antarctica were collected at Indian Antarctic station, Maitri (70.77°S, 11.73°E) from Dec 2013–Feb 2014. The individual particle analysis revealed that particles were mainly composed of Si, Fe, Al, Ca and Mg. Most of the particles were observed in layered, flattened, aggregated and glass-like shapes. The frequency distributions of the morphological parameters, AR and CIR were observed to be bimodal with respective mode peaks 1.3 and 1.9 for AR; 0.4 and 0.7 for CIR. The spectral refractive indices of individual particles were estimated. The imaginary part of the refractive indices was observed to be maximum for chromium (Cr) and iron (Fe) rich particle and nearly negligible for aluminum (Al) rich particle. At 0.58 μm wavelength, the difference in SSA with respect to Al rich particle was found to be maximum for Ca rich particles (i.e. 43%) followed with Cr and Fe rich particle (i.e. 42.08%) and Cr rich particle (i.e. 39.32%).