Observation and Analysis of Atmospheric Ice-Nucleating Particles in Online Continuous-Flow Diffusion Chamber in Winter in North China

In this paper, we measure ice-nucleating particle (INP) number concentrations at a mountain site on the northwestern margin of Beijing during the winter of 2017, which were obtained using a newly purchased continuous-flow diffusion chamber (BJ-CFDC). We analyzed the characteristics of the atmospheric INP number concentrations with respect to weather elements, the precipitation size distribution, and aerosol observations. We identified the relationships of the INP number concentration with activation temperature, super saturation with respect to water, and aerosol particles larger than 0.5 m. The results indicate that the atmospheric INP number concentration has a large variation with respect to different activation temperatures, ranging between 2.50–76.8 L⁻¹ at −20°C, with an average of 18.347 L⁻¹. The atmospheric INP number concentration was found to increase exponentially both with decreasing temperature and increasing super saturation with respect to water. The results also revealed that the atmospheric INP number concentration has a good correlation with the concentration of aerosol particles larger than 0.5 m. With this relation, the relevance of the predicted and measured INP number concentrations is greater than the relationship based only on temperature. The atmospheric INP number concentration in snow days was found to first increase and later decrease. That is, the INP number concentration increases when the snow begins, but the strong wind in the later snow period scavenges the aerosols, which leads to a reduced INP number concentration. With the BJ-CFDC, the first instrument of its kind in China, the results of this study will advance the study of orographic cloud and precipitation in winter in North China, as well as facilitate the development of cloud modeling and weather modification studies.