Seasonal variability of the aerosol parameters over Kanpur, an urban site in Indo-Gangetic basin

Abstract

With the growing antropogenic activities and urbanization, pollution level is found to be increasing in the Indo-Gangetic (IG) basin. This trend of increasing pollution has direct impact on the climatic conditions, especially the increase of haze, fog and cloudy conditions in the region. A ground-based CIMEL radiometer has been deployed on the campus of the Indian Institute of Technology (IIT) Kanpur, India, as a part of the Aerosol Robotic Network (AERONET) program with an objective to characterize the aerosols in the IG basin. The optical properties of the aerosols over Kanpur, which is one of the largest industrial cities in the IG basin, show strong seasonal and inter-annual variations. The fine mode urban/industrial aerosols contribute more than 75% to the observed aerosol optical depth (AOD) during the post-monsoon and winter seasons, whereas the natural dusts contribute ∼60% to the AOD during the pre-monsoon and monsoon seasons. Effective radius ( R eff) and volume weighted mean radius ( R V), the two best representative parameter of the coarse and fine modes of aerosol size distribution show maximum values during winter season. The increase in the R V is attributed to the hygroscopic growth of fine mode particles in presence of high relative humidity and favorable temperature condition; but the increase in r eff is due to the association of the fine mode absorbing particles to the coarser dusts. This is also reflected in low values (<0.8) of single scattering albedo (SSA) at coarse mode during the season. Higher values of SSA at fine mode indicate dominance of water-soluble aerosols scattering in nature. The linear regression equations between AOD (at 0.67 μm wavelength) and extinction coefficient due to fine and coarse modes also reveal the relative contribution of the fine and coarse mode particles to the observed optical properties during different seasons in Kanpur.