Information about the physical and chemical properties of atmospheric aerosol particles is essential for an improved understanding of the role of atmospheric aerosols on local to global climate. The hygroscopicity (ability to uptake water) of atmospheric aerosol particles has direct effects, which regulates the Earth’s radiation budget, and indirect effects leading to cloud formation and precipitation. This study introduces a novel method to investigate the mass-based hygroscopicity of the atmospheric aerosols over a wide range in sub-saturated regions using an advanced instrument called Quartz Crystal Microbalance with Dissipation monitoring (QCM-D). The mass-based hygroscopic understanding of the atmospheric aerosols is more relevant and scientifically informative than the size-based study since the mass of the aerosol particle is not expected to remain the same once it starts uptaking the water, unlike the size, which changes only after deliquescence. QCM is an extremely sensitive instrument that can monitor mass changes in the order of nanograms/cm2, and it considers water or any other liquid molecules coupled through hydration or entrapped in the cavities of the adsorbed film as additional mass. Sample aerosol particles from contrasting environments (polluted vs. cleaner) in different seasons are collected on a QCM sensor using MOUDI (Micro-Orifice Uniform Deposit Impactor) sampler, ensuring a uniform thin film. The change in mass is continuously monitored using QCM for a wide range of relative humidity (2–93%) values, and the mass-based hygroscopicity parameter, κ, is calculated for the potential use for the development of effective parameterizations to be used in the prognostic modeling.