Study on the Influence of Sulfuric Acid Plumes in Urban Residual Layers on High-Altitude New Particle Formation

Atmospheric new particle formation (NPF) has been recognized as a major contributor to aerosol and cloud condensation nuclei number concentrations, exerting substantial impacts on both air pollution and climate. However, NPF vertical distribution has been left largely uncharacterized because most, if not all, NPF observations were conducted on the ground surface, which may not be representative to the situation within the whole boundary layer. Here we conduct measurements on the vertical profiles of particle number size distribution and key precursors of NPF with a high payload tethered airship in Nanjing, China. We show that, while particle size distribution displays a homogeneous feature in a well-mixed boundary layer as expected, surprising particle nucleation is frequently seen at around 600 m altitude in early morning before the mixing layer is fully developed. The nucleation aloft is associated with sulfuric acid-rich plume, likely contributed by industrial emissions, yet its intensity is limited by low sulfuric acid clustering efficiency and low abundance of condensable organic vapors. Overall, our results reveal that industrial emission acts as an important source of urban sulfuric acid and nanoparticles, unrecognizable from ground-level measurement or in well-mixed atmosphere, and that the boundary layer dynamics has a profound influence on the vertical profiling of particle number size distribution.