In situ Study on Aerosol–Cloud Interactions in Upper Cloud Processes over the Yangtze River Delta

The aerosol–cloud interaction is essential for assessing the lifetime of clouds and aerosols as well as their climate effect. The current study on the aerosol–cloud interaction mainly focused on aircraft observation, satellite retrieval data, and modeling simulations, while fewer field observation experiments were carried out due to deployment difficulties, long experimental duration, and high instrument and labor consumption. As for the insufficient understanding of aerosol–cloud interactions, the aerosol–cloud observational data from field campaigns are extremely important. In this study, the authors conducted a field study on clouds and aerosols at the Mountain Daming station (located at an altitude of 1483 m) in the Yangtze River Delta. The study employed a fog monitor, a ground-based counterflow virtual impactor, a scanning mobility particle sizer, and so on. This study investigated the characteristics of cloud droplets and aerosols at the mountaintop during a cloudy period in July 2021 to discuss the impacts of aerosols on the formation, development, and scavenging effect of clouds. The removal rate was approximately 20%–50% during the initial stage of cloud formation. The authors found that higher supersaturation levels and larger aerosol particle sizes increased aerosol removal rates within clouds. This result indicates that particles of larger size were more inclined to activate as cloud condensation nuclei. By comparing three different stages of a single cloud event with various aerosol abundances, the authors discovered that a low aerosol load was advantageous for the formation of dense clouds with a high liquid water content, and the then cloud was composed of larger but fewer droplets. In contrast, increasing aerosol particles might lead to light clouds composed of numerous small droplets. Moreover, the authors further analyzed the size distribution of dry residual nuclei of cloud droplets with sizes of >8 μm. The results showed that these residual nuclei were mostly formed by aerosol particles with sizes of >100 nm. An increase in the concentration of aerosol particles within the same cloud event significantly decreased the number of cloud droplets with sizes of >8 μm and increased the diameter of cloud residual nuclei. These results indicate that an increase in aerosol particles can increase the number of cloud droplets and reduce the droplet diameter. Meanwhile, the critical activation diameter of aerosol particles became larger in water-limited clouds. Therefore, the authors concluded that the size distribution of aerosol particles significantly influenced the number and diameter of cloud droplets; conversely, the formation and development of clouds exhibit a certain scavenging effect on aerosols.