Characteristics of ice-nucleating particles in Beijing during Spring: a comparison study for the suburban and a nearby mountain area

Ice-nucleating particles (INPs) are of great importance for regional weather and climate by altering the microphysical properties of clouds. Large uncertainties still exist for the sources, abundance and variability of INPs over the polluted North China Plain (NCP) due to limited observations in this region and the complex physical and chemical properties of aerosols from multiple sources. In this study, the concentrations of INPs in the immersion freezing mode at temperatures ranging from -5 ℃ to -30 ℃ were simultaneously measured for about one month in the Spring season. The measurements were carried out at a mountain site and a suburb site in Beijing representing clean and anthropogenic condition, respectively. Different concentrations and characteristics of INP are found for the two sites, which reflect the influence of different the air masses and INP sources. Consistent with previous studies in this region, dust particles are found to be the most abundant INPs during the Spring season, and the contribution from anthropogenic pollution aerosols was of minor importance. Most interestingly, the INP concentration at the mountain site was about one magnitude higher than at the suburban site at temperatures higher than -10 ℃, which is caused by the primary biological aerosol from the forests in the moutain area. Our results characterize the important role of these bioaerosols, which are also expected to have a strong impact on the glaciation of orographic clouds.

In addition, to extend the data set, we investigated the characteristics of INPs in other seasons, to further study and quantify seasonal cycles of INP concentrations and sources.