Investigating three patterns of new particles growing to the size of cloud condensation nuclei in Beijing's urban atmosphere
2021
Abstract. The growth of newly formed particles with diameters from
∼ 10 nm to larger sizes was investigated in Beijing's urban
atmosphere during 10–23 December 2011, 12–27 April 2012, and
June–August 2014. In 11 out of 27 new particle formation (NPF) events
during June–August, the maximum geometric median diameter ( Dpgmax ) of
newly formed particles exceeded 75 nm, and the grown new particles may
contribute to the population of cloud condensation nuclei. In contrast, no
apparent growth in new particles with Dpgmax 20 nm was
observed in all of the events in December, in approximately half of the NPF
events in April, and in only two events during June–August. New particles observed
in the latter NPF events were too small to be activated as cloud
condensation nuclei. Apparent new particle growth with Dpgmax ≤ 50 nm was observed in the remaining 18 NPF events. The 11 NPF events during
June–August with Dpgmax exceeding 75 nm were analyzed in detail. The
particle growth patterns can be clearly classified into three types:
one-stage growth and two-stage growth-A and growth-B patterns. The one-stage growth
pattern is characterized by a continuous increase in Dpg with
Dpgmax ≥ 80 nm (4 out of 11 NPF events), and the two-stage growth-A
and growth-B patterns are characterized by no apparent growth and shrinkage
of particles, respectively, in the middle 2–4 h of the growth period (7 out
of 11 NPF events). Combining the observations of gaseous pollutants and
measured (or modeled) concentrations of particulate chemical species, the
three growth patterns were discussed in terms of the spatial heterogeneity
of NPF, formation of secondary aerosols, and evaporation of semivolatile
particulates. Secondary organic species and NH4NO3 were argued
to be two major contributors to the growth of new particles, but
NH4NO3 likely contributed to growth only in the late afternoon
and/or at nighttime.
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