Campaign for Direct In Situ Study of Residual Layer Chemistry in Urban Beijing

Abstract This paper introduces the Direct In Situ Study of Residual Layer Chemistry in Urban Beijing (DISRELCUB) experiment conducted on the roof of China International Trust and Investment Corporation (CITIC) tower, which stands 528 m above the ground in urban Beijing. The aim is to directly study in situ residual layer chemistry and its influence on the air quality on the ground surface. The experiments were performed during March–April 2022 and March–April 2024, respectively. For the first time, we can present a picture of the nanoparticle formation and growth owing to residual layer chemistry in a megacity. In the first part, we introduce the experimental design, the observation station, and the instruments; in the second part, we present boundary layer thermodynamics during observation periods as well as the characteristics of meteorological variables, aerosol, and trace gases measured on the 528-m platform, 143-m platform, and ground surface, respectively. In the third section, we show highlights of some key radical reservoir molecules and vapors associated with nanoparticle formation and growth on the 528-m platform; in the last part, we quantify the contribution of residual layer chemistry to the ground surface by turbulence with a large-eddy simulation model. Significance Statement New particle formation and growth in the boundary layer is of fundamental importance for air quality mitigation in urban atmospheres. The chemistry of the residual layer is a vital aspect of atmospheric chemistry, but the mechanism and atmospheric significance of aerosol formed by chemical processes in the residual layer remain poorly understood. With the deployment of extensive measurements on CITIC tower, we have the opportunity to elucidate the mechanisms behind new particle formation and growth triggered by residual layer chemistry, as well as their contribution to ground-level air quality. Herein, we primarily present the background and experimental design of the campaign along with some preliminary results.