New insights into the boundary layer revolution correlation with new particle formation characteristic in megacities of China

 New particle formation (NPF) event happened in the planetary boundary layer contribute more than 60% of ultrafine particles (UFP), which impact the could condensation nuclei (CCN) and the climate. This study retrieved the Particle Number Size Distribution (PNSD) and its relationship with Planetary Boundary Layer Height (PBLH), as well as nucleation mode aerosols trajectories during NPF events in three major Chinese cities: Beijing (BJ), Guangzhou (GZ), and Shanghai (SH). The observation periods include July 2017 to October 2019 (408 effective observation days), November 2019 to March 2020 (127 effective observation days), and April to June 2020 (44 effective observation days) for BJ, GZ, and SH, respectively. The results show that BJ exhibits the highest Number Concentration (PNC) at 2.05 × 10⁶ cm⁻³, while GZ records the highest NPF frequency at 25.98% GZ during the Covid 19 lockdown. In contrast, SH has the lowest PNC at 6.27 × 10⁵ cm⁻³ and the lowest NPF frequency (18.87%). An increase in the PBLH reduces the survival parameter (P), thereby promoting the occurrence of NPF events. A high nucleation-mode PNC also promotes the occurrence of NPF events. The sources of PNSD at the three cities exhibit distinct trajectories on NPF days. The main source of pollutants in BJ is Mongolia, located to the northwest. In GZ, the contribution mainly comes from Jiangxi and Fujian provinces to the northeast, while in SH, the source lies to the northwest. NPF frequencies consistently exceed 25%, predominantly in the northern regions of each site, indicating higher NPF levels in the north compared to the south. This research provides valuable insights for developing strategies to manage the atmospheric environment.