资源环境科技发展态势分析平台

The high frequency of new particle formation (NPF) events observed under polluted atmospheric conditions is still poorly understood. To improve our understanding of NPF and its effects, the particle number size distribution (3–1000 nm) and submicron particle chemical composition were measured from 4 November 2017 to 17 January 2018 in suburban Beijing. During this intense campaign, 22 NPF events were identified with a frequency of 29%, including 11 cases that occurred under “clean” conditions (C-NPF) and 11 cases that occurred under “polluted” conditions (P-NPF). The observed formation rate (J₃) and condensation sink were 4.6–148.9 cm⁻³·s⁻¹ and 0.01–0.07 s⁻¹, and the majority of NPF events occurred when the condensation sink (CS) values below 0.03 s⁻¹, indicating that condensation vapor likely constitutes the critical limiting factor for NPF events. The correlations between log J₃ and [H₂SO₄] that close to previous CLOUD experimental results in the majority of NPF events (68%) suggest the high nucleation rates (up to 100 cm⁻³·s⁻¹) would be attributed by the amines that enhancing sulfuric acid nucleation, while the reminding cases (32%) possibly attributed to the H₂SO₄-NH₃ clustering mechanism, which is supported by the theoretical expectations for H₂SO₄ nucleation with NH₃ simulated by the MALTE_BOX model. The observed growth rate varied from 4.9 to 37.0 nm·h⁻¹, with the dominant contribution (>60%) from sulfuric acid during the early phases of growth (~4 nm), which was also sufficient to explain the observed Q_GR for <10 nm particles in high Q_SO4 cases. While for the low sulfate production (Q_SO4 < 0.1 μg·m⁻³·h⁻¹) cases, Q_SO4 systematically underestimated Q_GR, and the Q_SO4/Q_GR ratio drops from 0.5 to 0.3 as particles grow from a 5–10 nm size range to a 15–20 nm size range, suggesting the condensation of organic compounds strengthened as the particles grew larger and dominated the growth from 4 nm up to climatically relevant sizes (>50 nm)