Spatio-temporally differentiated impacts of temperature inversion on surface PM2.5 in eastern China

Temperature inversion (TI) is one of the meteorological conditions that significantly affect regional air quality. Knowledge gap regarding the impacts of TI on surface PM₂.₅ in different topographies still existed. In the present study, the occurrence frequency, temperature lapse rate (TLR), depth, and the diurnal variations of TI, surface-based TI (SBTI), elevated TI (ElTI), and multiple layers of TIs (MultiTI) and their impacts on near-surface PM₂.₅ concentrations over eastern China that covers a range of topographies and climates, are systematically investigated based on global reanalysis ERA5 and the nationwide monitoring PM₂.₅ dataset from 2014 to 2020. TIs occurred mostly in the early morning. Different types of TIs present distinctive seasonal and spatial patterns. The majority of SBTIs and ElTIs occurred during nighttime in northern China and daytime in southern China, respectively, as the result of their formation mechanisms. SBTIs usually had larger TLR while ElTIs had deeper depth. SBTIs showed strong enhancement effects on PM₂.₅ concentration over the study domain while ElTIs showed more obvious impacts on northern nocturnal PM₂.₅. The peak time of PM₂.₅ was found around 18:00–22:00 LST, and TLR and depth of TIs are thought to be more relevant to PM₂.₅ peak concentration due to their coincident peak times. The strength of TIs is therefore more crucial in regulating PM₂.₅ than its occurrence frequency. Based on statistical analysis, our study provided a large picture of the generic spatiotemporal patterns of TIs and illustrated the impacts of different TIs on surface PM₂.₅ pollution on a diurnal basis. For a deeper understanding of the formation of PM₂.₅ pollution, more attention needs to be paid to the nocturnal PM₂.₅ not only at surface level but also at higher levels in the presence of TIs.