Spatio-temporal Patterns and Potential Sources of Absorbing Aerosols in the Fenwei Plain

Air quality has gradually improved in many parts of China; however, air pollution is become more severe in the Fenwei Plain. Using OMI/Aura OMAERUV L2 and PM2.5 data, spatial autocorrelation analysis and back trajectory modeling were used to explore the spatio-temporal patterns of absorptive aerosols over the Fenwei Plain, and the dominant types, transmission paths, and potential source areas were identified. The main results can be summarized as follows: ① Annual mean absorbing aerosol index (AAI) values increased between 2005 and 2019, with high period occurring in 2006, 2013, and 2017, with values exceeding 0.63. Xi'an and Linfen were identified as a 'high-high' cluster, with AAI showing poor spatial stability and a 15.3% increase in area over the past 15 years. In contrast, the area connecting Xi'an and Linfen, which occupies 24.2% of the total area of the region, was identified as a 'low-low' cluster, with a sharp drop of 6.2% in area; ② The Fenwei Plain has high AAI values across a large area in winter, exceeding 0.8 in Linfen and Xi'an, and 91.5% of the study area exceeding 0.6. Values were lower in spring (AAI>0.4) and autumn (AAI>0.3), with the lowest values occurring in summer. The atmospheric diffusion conditions in spring, autumn, and winter are poor, associated with anticyclonic high-pressure events. The observed high AAI values were significantly affected by atmospheric diffusion conditions, temperature, and precipitation; ③ Back trajectory and source contribution modeling showed that long-range transport of air masses from Xi'an and Linfen occurs from the northwest, and short-range transport air masses occurs from the east and south. Two long-range sand and dust source areas were determined (with northwestern and northern wind sources); two carbon source areas were identified (with eastern and southern wind sources); and one combined sand and carbon source area was identified (from the Loess Plateau). Of these sources, the northwestern wind source, the Loess Plateau, and the southern wind source have significant influence in Xi'an, and the eastern wind source and the Loess Plateau have a significant impact on Linfen. Linfen is little affected by the northwestern wind source and the dust from the northern wind source. Based on the spatial distribution of CO and its correlation with AAI, it is concluded that cardon in the dominant absorbent aerosol in Linfen dust and carbon are most important in Xi'an. © 2021, Science Press. All right reserved.