Impacts of new particle formation on aerosol cloud condensation nuclei (CCN) activity in Shanghai: case study
- 1Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Fudan-Tyndall Centre, Department of environmental science and engineering, Fudan University, Shanghai 200433, China
- 2South China Institute of Environmental Sciences, Ministry of Environmental Protection, Guangzhou 510655, China
- 3Atmospheric Environment Institute, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
- 4Key Laboratory of Region Climate–Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
- 5State Environmental Protection Key Laboratory of the Cause and Prevention of Urban Pollution Complex, Shanghai Academy of Environmental Sciences, Shanghai 200233, China
Abstract. New particle formation (NPF) events and their impacts on cloud condensation nuclei (CCN) were investigated using continuous measurements collected in urban Shanghai from 1 to 30 April 2012. During the campaign, NPF occurred in 8 out of the 30 days and enhanced CCN number concentration (NCCN) by a factor of 1.2–1.8, depending on supersaturation (SS). The NPF event on 3 April 2012 was chosen as an example to investigate the NPF influence on CCN activity. In this NPF event, secondary aerosols were produced continuously and increased PM2.5 mass concentration at a rate of 4.33 μg cm−3 h−1, and the growth rate (GR) and formation rate (FR) were on average 5 nm h−1 and 0.36 cm−3 s−1, respectively. The newly formed particles grew quickly from nucleation mode (10–20 nm) into CCN size range. NCCN increased rapidly at SS of 0.4–1.0% but weakly at SS of 0.2%. Correspondingly, aerosol CCN activities (fractions of activated aerosol particles in total aerosols, NCCN/NCN) were significantly enhanced from 0.24–0.60 to 0.30–0.91 at SS of 0.2–1.0% due to the NPF. On the basis of the κ-Köhler theory, aerosol size distributions and chemical composition measured simultaneously were used to predict NCCN. There was a good agreement between the predicted and measured NCCN (R2=0.96, Npredicted/Nmeasured=1.04). This study reveals that NPF exerts large impacts on aerosol particle abundance and size spectra; thus, it significantly promotes NCCN and aerosol CCN activity in this urban environment. The GR of NPF is the key factor controlling the newly formed particles to become CCN at all SS levels, whereas the FR is an effective factor only under high SS (e.g., 1.0%) conditions.