ABSTRACT
Atmospheric precipitation samples were collected in 2018, 2019, and 2021 in Beijing to study the concentrations and changes of the main metal elements and water-soluble ionsï¼ the wet deposition fluxes of heavy metals, water-soluble ions, dissolved inorganic nitrogen, and sulfur in the atmospheric precipitation and their impacts on the ecological environmentï¼ and the scavenging mechanisms of the typical precipitation to atmospheric pollutants during the study period. The results showed that the precipitation in Beijing during the study period was mostly neutral or alkaline, and the frequency of acid rain occurrence was very low, only accounting for 3.06%. The total concentrations of major metal elements in 2018, 2019, and 2021 were ï¼4 787.46 ±4 704.31ï¼, ï¼7 663.07 ±8 395.05ï¼, and ï¼2 629.13 ±2 369.51ï¼ µg·L-1, respectively. The total equivalent concentrations of ions in 2018, 2019, and 2021 were ï¼851.68 ±649.16ï¼, ï¼973.98 ±850.94ï¼, and ï¼644.31 ±531.16ï¼ µeq·L-1, respectively. The interannual changes in major metal elements and ions followed the order of 2019 > 2018 > 2021. The seasonal average total concentrations of major metal elements in spring, summer, autumn, and winter were ï¼9 624.25 ±7 327.92ï¼, ï¼4 088.67 ±5 710.14ï¼, ï¼3 357.68 ±3 995.64ï¼, and ï¼6 203.19 ±3 857.43ï¼ µg·L-1, respectively, and the seasonal average total equivalent concentrations of ions in spring, summer, autumn, and winter were ï¼1 014.71 ±512.21ï¼, ï¼729.83 ±589.90ï¼, ï¼724.35 ±681.40ï¼, and ï¼1 014.03 ±359.67ï¼ µeq·L-1, respectively, all presenting the order of spring > winter > summer > autumn. NO3- and SO42- were the main acid-causing ions in precipitation, whereas NH4+ and Ca2+ were the main acid-neutralizing ions. The wet deposition fluxes of the heavy metal Cd were very low [ï¼0.05 ±0.01ï¼ mg·ï¼m2·aï¼-1], only accounting for ï¼0.13 ±0.04ï¼% of the total wet deposition fluxes of main metal elementsï¼ however, its soil safety years were 291 years, significantly lower than those of other heavy metals, displaying that its ecological risk was relatively the highest. The total wet precipitation flux of water-soluble ions NH4+, Ca2+, NO3-, and SO42- accounted for ï¼85.72 ±2.18ï¼% of the wet precipitation flux of total ions, suggesting that their comprehensive impact on the ecological environment might have been higher. DIN wet deposition flux was mainly characterized by NH4+-N, which had a positive impact on the ecological environment in summer. SO42--S wet deposition flux was higher in summer, so its positive impact on the ecological environment was also greater. The scavenging effects of atmospheric precipitations to pollutants from the air were impacted by various factors, and the synergism effects of these factors could directly influence the scavenging mechanisms of precipitation to pollutants.
