27 Jun 2022
27 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Aerosol activation characteristics and prediction at the central European ACTRIS research station Melpitz, Germany

Yuan Wang1,2,3, Silvia Henning1, Laurent Poulain1, Chunsong Lu2, Frank Stratmann1, Yuying Wang2, Shengjie Niu2,4, Mira L. Pöhlker1, Hartmut Herrmann1, and Alfred Wiedensohler1 Yuan Wang et al.
  • 1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 2Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, 210044 Nanjing, China
  • 3Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, 730000 Lanzhou, China
  • 4College of Safety Science and Engineering, Nanjing Tech University, 210009 Nanjing, China

Abstract. Understanding aerosol particle activation is essential for evaluating aerosol indirect effects (AIEs) on climate. Long-term measurements on aerosol particle activation help to understand the AIEs and narrow down the uncertainties of AIEs simulation; however, they are still scarce. In this study, more than 4-year aerosol comprehensive measurements were utilized at the central European research station Melpitz, Germany, to gain insight into the aerosol particle activation and provide recommendations on improving prediction. The overall characteristics of aerosol particle activation at Melpitz are first summarized. For supersaturation (SS) levels of 0.1 %, 0.2 %, 0.3 %, 0.5 %, and 0.7 %, the mean cloud condensation nuclei (CCN) number concentration (NCCN) increases with the increase of SS from 513 to 2477 cm-3, which represents 11 % to 52 % of the total particle number concentration with diameter ranging from 10 to 800 nm, while the hygroscopicity factor (k) and the critical diameter (Dc) decrease from 0.28±0.08 (mean value ± one standard deviation) to 0.20±0.09 and from 177±19 to 54±8 nm, respectively. Aerosol particle activation is highly variable across seasons, especially at low SS conditions. At SS = 0.1 %, the seasonal mean NCCN is 681 cm-3 in winter, which is almost twice higher than the summer value (347 cm-3); the seasonal mean activation ratio (AR) in winter (0.18) is three times higher than the summer one. Subsequently, size dependency of both k and the state of mixing were investigated. As the particle diameter (Dp) increases, k increases at Dp of ~40 to 100 nm and almost stays constant at Dp of 100 to 200 nm, whereas the degree of the external mixture keeps decreasing at Dp of ~40 to 200 nm. The relationships of k vs. Dp and mixture degree vs. Dp were both fitted well by the power-law function for each season. Finally, we recommend applying the k - Dp power-law fit for NCCN prediction, which can narrow down the median uncertainty within 10 % for different SS conditions and seasons at Melpitz; it also could be applied to predict NCCN at other rural and continental regions with a similar aerosol background. Additionally, the mean k value over Dp of 100 to 200 nm also works well on the NCCN prediction when SS is less than 0.2 %.

Yuan Wang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-427', Anonymous Referee #1, 02 Aug 2022
  • RC2: 'Comment on acp-2022-427', Angela Buchholz, 02 Aug 2022

Yuan Wang et al.

Yuan Wang et al.


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Short summary
Aerosol particle activation affects cloud, precipitation, radiation, and thus the global climate. Its long-term measurements are important but still scarce. In this study, more than 4-year measurements at a central European station were analyzed. The overall characteristics and seasonal changes of aerosol particle activation are summarized. The power-law fit between particle hygroscopicity factor and diameter was recommended for predicting CCN number concentration.