The Relationship of Aerosol Properties and Ice‐Nucleating Particle Concentrations in Beijing.

This paper investigates immersion mode ice‐nucleating particle (INP) concentrations measured with a continuous flow diffusion chamber at temperatures of −20°C, −25°C, and −30°C in Beijing from 4 May to 4 June 2018. Aerosol conditions in the experiment period are classified into four types: clean, light PM2.5 pollution, heavy PM2.5 pollution, and dust. The PM mass concentrations and the aerosol size distributions are distinctly different in the four aerosol conditions. INP concentration increases as temperature decreases from −20°C to −30°C for all the four aerosol conditions. At a given temperature, INP concentrations progressively increase as the aerosol condition changes from clean to light PM2.5 pollution and to heavy PM2.5 pollution condition. At −25°C and −30°C, the dust condition has a much higher INP concentration than the other aerosol conditions. The INP concentration is closely related to the number concentration of aerosols with diameters of 1.0–2.5 μm (n1.0 ${n}_{1.0}$). Using a similar method as in the previous parameterization of INP concentrations for global and fairly clean aerosol conditions, a new parameterization of the INP concentration based on n1.0 ${n}_{1.0}$ is provided for the complicated aerosol conditions with high aerosol number concentrations in Beijing. Plain Language Summary: The ice‐nucleating particle (INP) concentrations and the aerosol–INP relationship under conditions with high aerosol number concentrations including anthropogenic sources are not well understood. In this study, measurements of aerosols and INPs under various aerosol conditions in Beijing are used to investigate the aerosol–INP relationship. It is found that the immersion mode INP concentration in the experiment period is not only dependent on temperature but also substantially influenced by aerosol conditions. At temperatures between −20°C and −30°C, the condition with the heavier PM2.5 pollution has the higher INP concentrations, and the dust condition has the highest INP concentrations. The number concentration of aerosols with diameters of 1.0–2.5 μm is a better parameter for predicting the INP concentration than the number concentration of aerosols with diameters of 0.5–2.5 μm, which was proposed to predict the INP concentration in previous studies under relatively clean aerosol conditions. The new parameterization of aerosol–INP relationship provided in this study can be applicable for complicated aerosol conditions with high aerosol number concentrations including anthropogenic sources. Key Points: The immersion mode ice‐nucleating particle concentration progressively increases from clean to polluted aerosol conditionNumber concentration of aerosols with diameters of 1.0–2.5 μm is closely related to immersion mode ice‐nucleating particle concentrationParameterization of immersion mode ice‐nucleating particle concentration is provided for condition with high aerosol number concentration [ABSTRACT FROM AUTHOR]