Evaluation of transport processes over North China Plain and Yangtze River Delta using MAX-DOAS observations

[摘要] Pollutant transport has a substantial impact on theatmospheric environment in megacity clusters. However, owing to the lack ofknowledge of vertical pollutant structure, quantification of transportprocesses and understanding of their impacts on the environment remaininadequate. In this study, we retrieved the vertical profiles of aerosols,nitrogen dioxide (NO 2 ), and formaldehyde (HCHO) using multi-axisdifferential optical absorption spectroscopy (MAX-DOAS) and analyzed threetypical transport phenomena over the North China Plain (NCP) and YangtzeRiver Delta (YRD). We found the following: (1) the main transport layers(MTL) of aerosols, NO 2 , and HCHO along the southwest–northeasttransport pathway in the Jing-Jin-Ji region were approximately 400–800,0–400, and 400–1200 m, respectively. The maximum transport flux of HCHOappeared in Wangdu (WD), and aerosol and NO 2 transport fluxes wereassumed to be high in Shijiazhuang (SJZ), both urban areas being significant sources feeding regional pollutant transport pathways. (2) The NCP was affected by severe dust transport on 15 March 2021. The airborne dust suppressed dissipation and boosted pollutant accumulation, decreasing the height of high-altitude pollutant peaks. Furthermore, the dust enhancedaerosol production and accumulation, weakening light intensity. For theNO 2 levels, dust and aerosols had different effects. At the SJZ andDongying (DY) stations, the decreased light intensity prevented NO 2 photolysis and favored NO 2 concentration increase. In contrast, dustand aerosols provided surfaces for heterogeneous reactions, resulting inreduced NO 2 levels at the Nancheng (NC) and Xianghe (XH) stations. Thereduced solar radiation favored local HCHO accumulation in SJZ owing to thedominant contribution of the primary HCHO. (3) Back-and-forth transboundarytransport between the NCP and YRD was found. The YRD-to-NCP and NCP-to-YRDtransport processes mainly occurred in the 500–1500 and 0–1000 m layers,respectively. This transport, accompanied by the dome effect of aerosols,produced a large-scale increase in PM 2.5 , further validating thehaze-amplifying mechanism.

[学科分类] 医学（综合）