New particle formation in the marine atmosphere during seven cruise campaigns
Authors: Zhu Yujiao , Li Kai , Shen Yanjie , Gao Yang , Liu Xiaohuan , Yu Yang , Gao Huiwang , Yao Xiaohong 
Published: January 2019

Abstract. We measured the particle number concentration, size distribution, and new
particle formation (NPF) events in the marine atmosphere during six cruise
campaigns over the marginal seas of China in 2011–2016 and one campaign from
the marginal seas to the Northwest Pacific Ocean (NWPO) in 2014. We observed
relatively frequent NPF events in the atmosphere over the marginal seas of
China, i.e., on 23 out of 126 observational days, with the highest frequency
of occurrence in fall, followed by spring and summer. In total, 22 out of 23
NPF events were found to be associated with the long-range transport of
continental pollutants based on 24 h air mass back trajectories and
pre-existing particle number concentrations, which largely exceeded the clean
marine background, leaving one much weaker NPF event that was likely induced
by oceanic precursors alone, as supported by multiple independent pieces of
evidence. Although the long-range transport signal of continental pollutants
can be clearly observed in the remote marine atmosphere over the NWPO, NPF
events were observed on only 2 out of 36 days. The nucleation-mode particles
(<30 nm), however, accounted for as high as 35 %±13 % of
the total particle number concentration during the NWPO cruise campaign,
implying the existence of many undetected NPF events in the near-sea-level
atmosphere or above. To better characterize NPF events, we introduce a term called the net
maximum increase in the nucleation-mode particle number concentration
(NMINP) and correlate it with the formation rate of new particles (FR). We find
a moderately good linear correlation between NMINP and FR at
FR≤8 cm−3 s−1, but no correlation exists at
FR>8 cm−3 s−1. The possible mechanisms are argued in terms of the roles of
different vapor precursors. We also find that a ceiling exists for the
growth of new particles from 10 nm to larger sizes in most NPF events. We
thereby introduce a term called the maximum geometric median diameter of new
particles (Dpgmax) and correlate it with the growth rate of new
particles (GR). A moderately good linear correlation is also obtained
between the Dpgmax and GR, and only GR values larger than
7.9 nm h−1 can lead to new particles growing with a Dpgmax
beyond 50 nm
based on the equation. By combining simultaneous measurements of the
particle number size distributions and cloud condensation nuclei (CCN) at
different super saturations (SS), we observed a clear increase in CCN when
the Dpg of new particles exceeded 50 nm at SS=0.4 %.
However, this case did not occur for SS=0.2 %. Consistent with the
results of previous studies in the continental atmosphere, our results imply
that particles smaller than 50 nm are unlikely activated as CCN at
SS=0.4 % in the marine atmosphere. Moreover, κ decrease from 0.4
to 0.1 during the growth period of new particles, implying that organics
likely overwhelm the growth of new particles to CCN size. The chemical
analysis of nano-Micro-Orifice Uniform Deposit Impactor (nano-MOUDI) samples reveals that trimethylamine (TMA) and oxalic
acid might appreciably contribute to the growth of new particles in some
cases.