Optical properties of atmospheric aerosols over the Ganges Valley Aerosol Experiment site, ARIES, Nainital

Description

The Atmospheric Radiation Measurement (ARM) first Mobile Facility (AMF1) has been operating at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, under the GVAX (Ganges Valley Aerosol Experiment) field campaign since June 2011. Under this project, the aerosol observing system (AOS) that comprises a set of instruments designed primarily for the continuous measurements of optical and microphysical properties of atmospheric aerosol at the surface is in operation. The principal measurements are those of the aerosol absorption and scattering coefficients, backscattered radiation, concentration, cloud condensation nuclei, particle number concentration, and particle size distribution as a function of the particle size and radiation wavelength. These measurements are used for calculating the aerosol single-scattering albedo (SSA), asymmetry parameter (g), and hygroscopic growth factor, and those are used for radiative forcing estimation. Generally, the low values of light scattering and hemispheric backscattering coefficients are observed during the Indian summer monsoon period, and it showed increasing trend after the monsoon. Total scattering and hemispheric back scatter coefficients at 450 and 700 nm are about 80% of the value at 550 nm respectively, and most of the particle concentration ranges from 200 to 5000 cm-3 during the study period. Such values are typical for a high-altitude site. The light scattering coefficients have strong positive correlation with hemispheric backscattering coefficients. The hemispheric backscatter ratio ranged from 0.1 to 0.15 during the period under study. The estimated Ångström exponent (indicates about the size of particles) ranges from 0.8 to 1.5, indicating the dominance of fine particles over the site. The single-scattering albedo obtained during this period ranged from 0.7 to 0.9. Detailed discussion will be made during the presentation.