Organic aerosols (OA) represent a major fraction of the atmospheric aerosols and are known to have profound impact on cloud and precipitation forming processes and eventually on Earth’s radiative balance. The formation and atmospheric evolution of OA, however, remains poorly characterized resulting in biased estimations of global secondary OA (SOA) budget in climate models. In part, this uncertainty is attributed to the lack of ambient measurements of aerosol physical and chemical properties. Constituting ~18% of the world’s total population, India is one important yet understudied region where chemical properties of aerosols are expected to have much impact on cloud and precipitation processes. Therefore, measurements of aerosol properties are essential under contrasting environment to enhance our understanding about the sources and chemical evolution of OA and validate the chemical climate model. Here, I present the results from a month-long field campaign conducted at a coastal metropolitan site Chennai during Jan-Feb 2019. Online continuous measurements of NR-PM1 (Non refractory particulate matter less than 1 micro meter) have been carried out using Aerosol Chemical Speciation Monitor (ACSM) accompanied by black carbon (BC) observations. Back trajectory analysis using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model enabled the classification of air masses sampled in to two periods: “Mixed period” and “clean marine period”. Source apportionment studies using Positive Matrix Factorization (PMF) revealed equal contribution of primary and secondary OA factors to the total OA mass during mixed period. Whereas, during the clean marine period with prevailing marine winds, secondary formation dominated the total OA mass by constituting ~82%. Further, thermodynamic model is used to predict aerosol liquid water (ALWC) and the effect of ALWC as well as marine winds on aerosol composition and SOA formation is explored for both the periods.