<p><strong>Abstract.</strong> The growth of newly formed particles with diameters from ~ 10 nm to a larger size was investigated in Beijing's urban atmosphere on 10–23 December 2011, 12–27 April 2012 and through June–August 2014. The maximum geometric median diameter (D<sub>pgmax</sub>) of newly formed particles in 11/27 new particle formation (NPF) events through June–August 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 D<sub>pgmax</sub> < 20 nm was observed in all of the events occurring in December, in approximately half of the NPF events occurring in April and only 2/27 of the NPF events occurring in 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 D<sub>pgmax</sub> ≤ 50 nm was observed in the remaining NPF events. The 11/27 NPF events with D<sub>pgmax</sub> exceeded 75 nm were thereby analyzed in-depth. They are clearly three particle growth pattern classifications: one-stage growth, which is characterized by a continuous increase in D<sub>pgmax</sub> ≥ 80 nm (4/11 NPF events), and two-stage growth-A and growth-B, which are characterized by either no apparent growth (two-stage growth-A) or a shrinkage of particles (two-stage growth-B) in the middle 2–4 hours of the growth period (7/11 NPF events). Combining the observations of gaseous pollutants and the measured (or modeled) concentrations of particulate chemical species, the three growth patterns were discussed in terms of the spatial heterogeneity of NPF, the formation of secondary aerosols and the evaporation of semi-volatile particulates. Secondary organic species and NH<sub>4</sub>NO<sub>3</sub> were argued to be two major contributors to the growth in new particles, but NH<sub>4</sub>NO<sub>3</sub> likely contributed to growth only in the late afternoon and/or at nighttime.</p>

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.