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New particle formation (NPF) events and their impacts on cloud condensationnuclei (CCN) were investigated using continuous measurements collected inurban Shanghai from 1 to 30 April 2012. During the campaign, NPF occurred in8 out of the 30 days and enhanced CCN number concentration (NCCN) by afactor of 1.2–1.8, depending on supersaturation (SS). The NPF event on 3April 2012 was chosen as an example to investigate the NPF influence on CCNactivity. In this NPF event, secondary aerosols were produced continuouslyand 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 onaverage 5 nm h−1 and 0.36 cm−3 s−1, respectively. The newlyformed particles grew quickly from nucleation mode (10–20 nm) into CCN sizerange. NCCN increased rapidly at SS of 0.4–1.0% but weakly at SS of0.2%. Correspondingly, aerosol CCN activities (fractions of activatedaerosol particles in total aerosols, NCCN/NCN) were significantlyenhanced from 0.24–0.60 to 0.30–0.91 at SS of 0.2–1.0% due to the NPF. Onthe basis of the κ-Köhler theory, aerosol size distributions andchemical 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 studyreveals that NPF exerts large impacts on aerosol particle abundance and sizespectra; thus, it significantly promotes NCCN and aerosol CCN activity inthis urban environment. The GR of NPF is the key factor controlling thenewly formed particles to become CCN at all SS levels, whereas the FR is aneffective factor only under high SS (e.g., 1.0%) conditions

Impacts of new particle formation on aerosol cloud condensation nuclei (CCN) activity in Shanghai: case study