Chemical compositions vary between and within particles due to the complex sources and aging processes, causing particle-to-particle heterogeneity in aerosol hygroscopicity, which is of great importance to aerosol climatic and environmental effects. This study proposes an algorithm to quantify the heterogeneity from in situ measurements, sheds light on the reanalysis of the existing H-TDMA datasets, and could have a large impact on how we use and think about these datasets.