Chemical compositions in an aerosol polulation can generally be classified into the nearly hydrophobic (NH), the less hygroscopic (LH), and the more hygroscopic (MH) components according to their capacities of water absorption. The distribution of these three components varies between and within particles due to the complex sources and aging processes, causing the particle-to-particle heterogeneity in aerosol hygroscopicity. Although this heterogeneity is of great importance to the evaluation of aerosol climatic and environmental effects, it has not been paid attention to in previous studies. This study proposes an algorithm to quantify the particle-to-particle heterogeneity from in-situ measurements for the first time. This algorithm can efficiently characterize the evolution of aerosol heterogeneity with time in the atmosphere and provide a framework for quantifying heterogeneities to merge observations into numerical models to deeply investigate how heterogeneity in aerosol hygroscopicity influences aerosol effects on climate and environment.