The number concentrations of cloud condensation nuclei (CCN) and submicron aerosols (CN), along with their chemical composition and optical properties, have been studied during October 2008, October-November 2009 and November 2010 from an urban (Kanpur) site in the Indo-Gangetic Plain (IGP). The concentrations of CCN and CN and their optical properties vary with primary emission and secondary aerosol formation. The CCN (at 0.38% super-saturation) and CN concentrations varied from ~3900 to 15,000cm-3 and ~23,000 to 99,000cm-3, respectively. The diurnal variability of CCN and CN show peak concentrations during early morning hours (6:00-9:00 AM) and nighttime (7:00-10:00 PM), attributable to variability in source strength of carbonaceous aerosols and secondary aerosol formation. The CCN and CN concentrations are ~50% higher during nighttime with simultaneous increase in organic carbon (OC), elemental carbon (EC) and NO3- mass concentrations. However, CCN/CN ratios are similar during day and nighttime suggesting their co-variability with primary and secondary aerosol formation. The CCN/CN ratios are relatively lower (range: 0.11-0.33) than global average value and those over urban areas (with similar chemical composition in China and around the world) suggesting suppressed activation and hygroscopic growth in highly polluted environment of the IGP. The average mass absorption efficiency of EC during daytime (11.7±2.5m2g-1) is about factor of two higher than that during nighttime (5.7±1.3m2g-1). These results have implications to study morphological features, mixing state and microphysical properties of aerosols under high acidic environment over northern India. © 2014 Elsevier Ltd.