Non‐Negligible Effects of Transport on Particle Number Concentration During Regional New Particle Formation Events

Abstract Transport plays a significant role in non‐regional new particle formation (NPF) events but is often overlooked in regional NPF events, particularly in typical banana‐shaped NPF events. This study applied a population balance method incorporating the transport (TR) effect to examine transport influence in three distinct regional (banana‐shaped) NPF events and one non‐regional NPF event in the Pearl River Delta region. In the non‐regional NPF event, particle changes due to transport closely align with observed particle concentration trends. In regional NPF events, the role of transport is also significant and cannot be overlooked. During the initial phase of NPF, transport exerts a positive effect, leading to an increase in particle concentration. However, as the boundary layer height increases, possible enhanced dilution led to a transition to a negative effect, resulting in particle loss. Ultimately, transport has a net positive effect in local new particle formation events, with the average contribution to particle concentration changes ranging from 47% to 68% across different cases. Incorporating the transport (TR) term reduced the root mean square error (RMSE) between simulated and observed particle number concentrations ( N CN ) by 28%–55% and increased the average coefficient of determination ( R 2 ) from 0.82 to 0.93 across the three cases. Moreover, including the TR term improved estimates of CCN concentration at 1.0% supersaturation (SS), though deviations persisted due to variations in background particle concentrations. Future studies should further investigate the size‐dependent influence of transport and its potential impact on CCN activation under lower SS to better constrain transport‐related processes in regional NPF events.