Precipitation can lead to significant leaching of heavy metals from abandoned tailings，resulting in a decline in the quality of the surrounding environment. This study aimed to simulate and quantify the migration patterns and fate of heavy metals in tailings caused by precipitation in various environmental media (tailings, air, water, soil, and sediments) using leaching tests, source apportionment, and a fugacity model. Results revealed that the average contents of Cd, Cu, As, Pb, Zn, and Cr in the un-weathered tailings were 3.43, 495.56, 160.70, 138.94, 536.57, and 69.52 mg/kg, respectively. The ecological risk factors in the tailings as well as in sediments and soils, were in the following order: Cd >Cu >As >Pb >Zn >Cr. A fugacity model based on the mass-balance methods was established, achieving a good agreement between simulation and measured values. The total amounts of Cd, Cu, As, Pb, and Zn leached from abandoned tailings over the 30-year evaluation period were estimated to be 1.09, 62.44, 0.16, 0.94, and 102.12 t, respectively. Soil and sediments are important reservoirs for heavy metals. The sum of the As, Cd, Cu, Pb, and Zn storage capacities in the soil and sediment accounted for 77.28%, 75.63%, 73.94%, 69.39%, and 57.80% of the total storage capacity, respectively. This study could provide the means for the establishment of a targeted pollution control plan, a guide for restoration projects, and will aid in controlling pollution risk and improving the surrounding environment.

Measurements of surface ozone (O₃), PM_2.5 and its major secondary components (SO${}_{\mathrm{4}}^{\mathrm{2}-}$ , NO${}_{\mathrm{3}}^{-}$ , NH${}_{\mathrm{4}}^{+}$ , and organic carbon (OC)), mixing layer height (MLH), and other meteorological parameters were made in the North China Plain (NCP) during the warm season (June–July) in 2021. The observation results showed that the summertime regional maximum daily 8 h average ozone (MDA8 O₃) initially increased and reached the maximum value (195.88 µg m⁻³) when the MLH ranged from approximately 900 to 1800 m, after which the concentration of O₃ decreased with further increase in MLH. Interestingly, synchronous increases in PM_2.5 concentration along with the development of the mixing layer (MLH <1200 m) were observed, and the positive response of PM_2.5 to MLH was significantly associated with the increase in SO${}_{\mathrm{4}}^{\mathrm{2}-}$ and OC. It was found that this increasing trend of PM_2.5 with elevated MLH was driven not only by the wet deposition process but also by the enhanced secondary chemical formation, which was related to appropriate meteorological conditions (50 % < RH <70 %) and increased availability of atmospheric oxidants. Air temperature played a minor role in the change characteristics of PM_2.5 concentration, but it greatly controlled the different change characteristics of SO${}_{\mathrm{4}}^{\mathrm{2}-}$ and NO${}_{\mathrm{3}}^{-}$ . The concentrations of PM_2.5, its major secondary components, and the oxidation ratios of sulfate (SOR) and nitrate (NOR) increased synchronously with elevated MDA8 O₃ concentrations, and the initial increase in PM_2.5 along with increased MLH corresponded well with that of MDA8 O₃. We highlight that the correlation between MLH and secondary air pollutants should be treated with care in hot weather, and the superposition-composite effects of PM_2.5 and O₃ along with the evolution of mixing layer should be considered when developing PM_2.5–O₃ coordinated control strategies.