Vertical characteristics and potential sources of aerosols over northeast China using ground-based MAX-DOAS

Information on the vertical distribution of air pollutants is essential to understand the potential mechanisms of haze pollution. Multiaxial differential optical absorption spectrometry (MAX-DOAS) is an effective method to detect the vertical distribution of air pollutants. In this study, we used MAX-DOAS to continuously analyze the vertical aerosol distribution throughout the year (from January 2019 to December 2019) in Shenyang. In winter, the aerosol extinction coefficient (AEC) was the highest (0.63 +/- 0.09 km-1), followed by summer (0.53 +/- 0.08 km-1), spring (0.51 +/- 0.08 km-1), and autumn (0.47 +/- 0.09 km-1). The aerosol extinction coefficients in various seasons were affected by the weather type. The hygroscopic growth of small particles lead to a surface AEC reaching 1.45 +/- 0.23 km-1 in summer, resulting in heavy haze. The coal burning for heating and automobile exhaust in winter increased the possibility of winter haze, wherein the surface AEC can reach 1.27 +/- 0.19 km-1. Signs of aerosol transport can be observed at high latitudes in summer, and when combined with backward trajectories, the transport of pollutants from Inner Mongolia to Liaoning Province is evident. The possible sources of air pollutants were investigated using a concentration weighted trajectory (CWT) model. In addition to the nearby Liaoning Province, both Beijing and Tianjin were also the main sources of pollution in Shenyang (0.04 km; Shandong Province was the main source of pollution at 0.44 km).