Characteristics of Immersion Freezing Ice Nucleating Particles During Dust Season in Beijing

Abstract Atmospheric dust is a primary source of ice nucleating particles (INPs), yet their concentrations at temperatures warmer than −20°C are not fully characterized during Asian dust events. This study uses a membrane filtering method to collect aerosol samples and a droplet freezing method to measure daily immersion‐mode INP concentrations in Beijing during the dust season throughout March 2022. Daily aerosol samples are categorized into low, moderate, and heavy dust conditions using volume depolarization ratios from a Micro Pulse Lidar (MPL). Observed INP spectra exhibit a day‐to‐day variability of up to two orders of magnitude at a given temperature. The INP spectra can generally be fitted with a two‐mode distribution. We find that INP concentration correlates strongly with the mass concentration of coarse aerosols (PM coarse ), but weakly with that of fine aerosols. We therefore develop a PM coarse ‐based INP parameterization that is applicable to the mixed‐phase cloud temperature range (−3.5°C to −23.5°C). The parameterization scheme is validated using several independent measurements in the Beijing region. It offers a practical approach for estimating INP concentrations at relatively warm temperatures in atmospheric models by utilizing routinely available PM coarse data from air‐quality monitoring networks or chemical transport models. Heat treatment tests reveal that more than 50% of INPs are heat‐sensitive, indicating that biological or other heat‐sensitive materials may significantly contribute to INP concentrations, particularly at warmer temperatures.