Sources and vertical distribution of PM_2.5 over Shanghai during the winter of 2017

Shanghai, a metropolitan city in China, has suffered from severe air pollution, especially PM_2.5, in the last few years. Up to now the contribution of local emission and regional transport to the formation of haze in Shanghai remains unclear. With an aim to characterize the mechanism of haze formation in Shanghai, the present paper attempted to provide an overview of a tethered balloon-based field campaign. According to the backward trajectories, the air mass traveling slowly from Jiangsu province accounted for the highest PM_2.5 concentration (66 ± 20 μg/m³). Seventy vertical profiles of PM_2.5, NO, NO₂, SO₂ and O₃ within 1000 m were obtained, through which a comparison study on the characteristics of the vertical distributions of air pollutants on clean days and haze days was conducted. When altitude increased, clearly decreasing pattern of PM_2.5, NO, and NO₂ was observed during the field campaign. Due to the low atmospheric boundary layer, the diffusion of air pollutants was suppressed, which favored the formation of haze. The results of the generalized additive model revealed NO₂ could the most significant factor influencing the vertical distribution of PM_2.5 in both clean and haze days. This study provides new insight into the sources and vertical distribution of PM_2.5, which could offer references for air pollution modeling.