This book focuses on the optical properties of atmospheric aerosols, their diurnal and seasonal variations that have been observed at Kannur (11.9oN, 75.4oE, 5 m ASL). This work has been carried out with the ground based measurements by using a sun photometer. Measurement of aerosol mass loading and chemical analysis for identifying and quantifying various inorganic chemical species gives more insight to formulate a model suited for this region. The results were quite positive in climate models to study the impact of aerosols on the atmospheric radiation balance. The results of the chemical analysis conducted for aerosols of size < 10 μm collected using a high volume sampler are highlighted. In addition to these, the measured AOD together with the derived aerosol optical properties are incorporated in SBDART model to retrieve short wave radiative forcing at the top of the atmosphere and the surface. Along with the results of ground based observation, the effects of firework festival on the aerosol optical depth are discussed extensively. Further, a sun photometer working in UV region was constructed and this was used to monitor the interaction of aerosols in solar UV region.