Abstract
The aerosol size distribution and cloud condensation nuclei (CCN) number concentration were measured using a wide-range particle spectrometer (WPS) and a cloud condensation nuclei counter (CCNC) on Mt. Tian from 31 July to 9 September, 2019. Combined with meteorological data, distribution characteristics of aerosol size and CCN and their influencing factors were analyzed. The results indicated that the mean aerosol number concentration was 5475.6 ± 5636.5 cm−3. The mean CCN concentrations were 183.7 ± 114.5 cm−3, 729.8 ± 376.1 cm−3, 1630.5 ± 980.5 cm−3, 2162.5 ± 1345.3 cm−3, and 2575.7 ± 1632.9 cm−3 at supersaturation levels of 0.1%, 0.2%, 0.4%, 0.6%, and 0.8%, respectively. The aerosol number size distribution is unimodal, and the dominant particle size is 30–60 nm. Affected by the height of the boundary layer and the valley wind, the diurnal variation in aerosol number concentration shows a unimodal distribution with a peak at 17:00, and the CCN number concentration showed a bimodal distribution with peaks at 18:00 and 21:00. The particle size distribution and supersaturation have a major impact on the activation of the aerosol into CCN. At 0.1% supersaturation (S), the 300–500 nm particles are most likely to activate to CCN. Particles of 100–300 nm are most easily activated at 0.2% (S), while particles of 60–80 nm are most likely activated at high supersaturation (≥0.4%). The concentrations of aerosol and CCN are higher in the northerly wind. Ambient relative humidity (RH) has little relationship with the aerosol activation under high supersaturation. According to N = CSk fitting the CCN spectrum, C = 3297 and k = 0.90 on Mt. Tian, characteristic of the clean continental type.
Highlights
Aerosols can be activated into cloud condensation nuclei (CCN) or ice nuclei at cloud supersaturation (S), participate in cloud microphysical processes, and affect clouds and precipitation [1,2,3]
The case of most likely to activate to CCN at low supersaturation and 60–80 nm particles at high supersaturation
Nm particles were all most likely to activate to 80 nm particles were all most likely to activate to CCN at different relative humidity (RH) values
Summary
Aerosols can be activated into cloud condensation nuclei (CCN) or ice nuclei at cloud supersaturation (S), participate in cloud microphysical processes, and affect clouds and precipitation [1,2,3]. The size and chemical composition of aerosols determine whether they can be activated into CCN or ice nuclei [4,5,6]. Atmosphere 2020, 11, 912 aerosol-CCN-cloud-climate connections [7,8]. The indirect radiative forcing effect of the aerosol is the most uncertain factor in climate modeling and prediction [9], largely due to insufficient understanding of the aerosol nucleation properties. Measurement of aerosols and assessment of their ability to activate as CCN is significant, helping to further facilitate our understanding of the impacts of aerosols on regional and global climate. Model parameterizations for CCN prediction have been carried out in many regions by using particle size distribution, chemical composition, and hygroscopicity [13,14,15,16]. CCN activated in marine boundary layer clouds were strongly influenced by entrainment from the free troposphere [23]
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