Work

Nucleation and growth of sub-3 nm particles in the polluted urban atmosphere of a megacity in China

Year: 2016

Type: article

Abstract: . Particle size distribution down to 1.38 nm was measured in the urban atmosphere of Nanjing, China in spring, summer and winter during 2014–2015. Nucleation event occurred on 42 out of total 90 observation days, but new particles could grow to cloud condensation nuclei (CCN)-active sizes on only 9 days. In summer, infrequent nucleation was limited by both unfavorable meteorological conditions (high temperature and RH) and reduced anthropogenic precursor availability due to strict emission control measures during the 2014 Youth Olympic Games in Nanjing. The limiting factors for nucleation in winter and spring were meteorological conditions (radiation, temperature, and RH) and condensation sink, but for the further growth of sub-3 nm particles to CCN-active sizes, anthropogenic precursors again became limiting factors. Nucleation events were strong in the polluted urban atmosphere. Initial J1.38 at the onset and peak J1.38 at the noontime could be up to 2.1 × 102 and 2.5 × 103 cm−3 s−1, respectively, during the 8 nucleation events selected from different seasons. Time-dependent J1.38 usually showed good linear correlations with a sulfuric acid proxy for every single event (R2 = 0.56–0.86, excluding a day with significant nocturnal nucleation), but the correlation among all the 8 events deteriorated (R2 = 0.17) due to temperature or season change. We observed that new particle growth rate did not increase monotonically with particle size, but had a local maximum up to 25 nm h−1 between 1–3 nm. The growth rate behavior was interpreted in this study as the solvation effect of organic activating vapor in newly formed inorganic nuclei using nano-Köhler theory.

Source: Atmospheric chemistry and physics

DOI: 10.5194/acp-16-2641-2016