Abstract. The contribution of new particle formation (NPF) to cloud condensation
nuclei (CCN) number concentration (NCCN) varies largely under different
environments and depends on several key factors such as formation rate (J),
growth rate (GR), distribution of preexisting particles, and properties of
new particles during NPF events. This study investigates the contribution of
NPF to the NCCN and its controlling factors based on measurements
conducted at the Heshan supersite, in the Pearl River Delta (PRD) region of
China during fall 2019. The size-resolved cloud condensation nuclei
activity and size-resolved particle hygroscopicity were measured by a cloud
condensation nuclei counter (CCNc) and a hygroscopic tandem differential
mobility analyzer (HTDMA), respectively, along with a scanning mobility
particle sizer (SMPS) and a diethylene glycol scanning mobility particle
sizer (DEG-SMPS) for particle number size distribution (PNSD). A typical NPF
event on 29 October was chosen to investigate the contribution of the
NPF to NCCN under several supersaturation (SS) ratios. Two particle
properties (hygroscopicity and surface tension) affect CCN activation with
the latter being more important in terms of the CCN concentration
(NCCN). A lower value of surface tension (i.e., 0.06 N m−1) than the
pure-water assumption (0.073 N m−1) could increase the NCCN at
SS = 1.0 % by about 20 % during the nonevent period and by about 40 % during the event. In addition, an earlier peak time corresponding to a lower
critical diameter (D50) was also observed. The results show that high
formation rate, growth rate, and low background particle concentration lead
to high number concentrations of newly formed particles. The high growth
rate was found to have the most significant impact on the NCCN, which
can be attributed to the fact that a higher growth rate can grow particles
to the CCN size in a shorter time before they are scavenged by preexisting
particles. Two other NPF events (an event on 18 October in this
campaign and an event on 12 December 2014 in Panyu) were chosen to
perform sensitivity tests under different scenarios (growth rate, formation
rate, and background particle concentration). The calculated NCCN at
SS = 1.0 % on 12 December 2014 was significantly lower than that
from the other two events. The event on 12 December was re-simulated
using the growth rate taken from the event on 18 October which
resulted in similar CCN concentrations between the two events (12 December and 18 October), implying that the growth rate is the major
impact factor for CCN activation. Our results highlight the importance of
growth rate and surface tension when evaluating the contribution of NPF to
the NCCN.