Chemistry of new particle formation and growth events during wintertime in suburban area of Beijing: Insights from highly polluted atmosphere

Abstract

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 QGR for <10 nm particles in high QSO4 cases. While for the low sulfate production (QSO4 < 0.1 μg·m−3·h−1) cases, QSO4 systematically underestimated QGR, and the QSO4/QGR 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)