23 Jan 2023
 | 23 Jan 2023

The variation of particle number size distribution during the rainfall: wet scavenging and air masses changing

Guangdong Niu, Ximeng Qi, Liangduo Chen, Lian Xue, Shiyi Lai, Xin Huang, Jiaping Wang, Xuguang Chi, Wei Nie, Veli-Matti Kerminen, Tuukka Petäjä, Markku Kulmala, and Aijun Ding

Abstract. Below-cloud wet scavenging is an important pathway to remove atmospheric aerosols. The below-cloud wet scavenging coefficient (BWSC) is the value to describe the ability of rainfall to remove aerosols. The reported BWSCs obtained from the field measurements are much higher than the theory, but the reason for this remains unclear. In this study, based on the long-term field measurements in the Yangtze River Delta of eastern China, we find 28 % of the rainfall events are high BWSC events. The high BWSC events show the sudden decrease of particle number concentration in all size bins near the end of rainfall. By investigating the circulation patterns, backward trajectories and the variations of simultaneously observed atmospheric components, we find the cause of the high BWSC events is the air masses changing but not the wet scavenging. The change of air masses is always followed by the rainfall processes and cannot be screened out by the traditional meteorological criteria, which would cause the overestimation of BWSC. After excluding the high BWSC events, the observed BWSC is close to the theory and is correlated with the rainfall intensity and particle number concentrations prior to rainfall. This study highlights the discrepancy between the observed BWSC and the theoretical value may not be as large as it is currently believed. To obtain reasonable BWSCs and parameterization from field measurements, the effect of air masses changing during rainfall needs to be carefully considered.

Guangdong Niu 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 egusphere-2023-33', Anonymous Referee #1, 06 Feb 2023
    • AC1: 'Reply on RC1', Ximeng Qi, 29 May 2023
  • RC2: 'Comment on egusphere-2023-33', Anonymous Referee #2, 04 Apr 2023
    • AC2: 'Reply on RC2', Ximeng Qi, 29 May 2023

Guangdong Niu et al.


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Short summary
The reported below-cloud wet scavenging coefficients (BWSCs) are much higher than the theory, but the reason of it remains unclear. Based on the long-term observation, we find the air masses changing during the rainfall events causes the overestimation of BWSCs. Thus, the discrepancy in BWSCs between observation and theory is not as large as currently believed. To obtain reasonable BWSCs and parameterizations from field observations, the effect of air masses changing needs to be considered.