城市湖泊影响城市低空大气污染物时空分布的机制

Impact mechanisms of urban lakes on spatiotemporal distribution of lower atmospheric pollutants in urban environments

摘要:

湖泊在调节局地气候和空气质量方面发挥着重要的作用,城市湖泊对城市局地大气边界层环流和大气污染物输送机制的影响是目前城市空气质量研究的重要问题。本文分析了夏季南京城区濒湖站近地面大气污染物质量浓度的日变化特征,并与相对远离湖泊的非濒湖站的观测结果进行比较。结果表明:对于以近地面排放为主的NO₂,日间濒湖站平均质量浓度比非濒湖站高(1.64±0.29)μg·m^-3,夜间则低(0.51±1.39)μg·m^-3;以边界层中高层生成与传输为主的O₃,呈现出与NO₂相反的趋势,日间濒湖站平均质量浓度比非濒湖站低(9.57±2.19)μg·m^-3,夜间则高(1.24±4.68)μg·m^-3;PM_2.5质量浓度的差值没出现类似特征。利用二维陆面过程模式,并结合不同排放情景,对湖泊-城市陆地分布进行敏感性数值试验。试验结果表明,城市区域内湖面与陆面的热力性质差异影响了低空大气环流和垂直热力稳定度,并进一步影响城市近地面大气污染浓度的扩散传输过程。受湖泊存在的影响,白天位于湖泊及濒湖区域上方的垂直大气热力稳定度高于非濒湖区域上空,低层大气垂直扩散较弱,导致濒湖区域以近地面排放为主的污染物比质量浓度偏高,而以边界层中高层排放与生成为主的污染物比质量浓度则偏低;夜间情况则与之相反。该试验结果与观测数据的变化趋势吻合,且与WRF-Chem模拟结果类似。

Abstract:

Rapid urbanization in China has exacerbated atmospheric pollution, particularly in urban areas.Urban lakes played a crucial role in moderating local climate and air quality by influencing atmospheric boundary layer circulation and pollutant transport mechanisms.However, previous studies have relied primarily on mesoscale models, where the influence of additional coupled mechanisms may impact the accuracy of sensitivity results.To address this, we utilized a conceptual urban land surface model to conduct suburban-scale sensitivity experiments, isolating the primary factors and mechanisms by which urban lakes influence the distribution and transport of near-surface pollutants.Focusing on the diurnal patterns of pollutant mass concentrations at lakeside and non-lakeside urban stations in Nanjing during the summer, we found notable differences in pollutant behavior.For NO₂, a ground-emitted pollutant, lakeside stations recorded a daytime average concentration of (1.64 ±0.29) μg·m^-3 higher than non-lakeside, while nighttime concentrations were (0.51 ±1.39) μg·m^-3 lower.In contrast, O₃, which forms at mid-and upper-boundary layers, exhibited lower daytime concentrations by (9.57 ±2.19) μg·m^-3 at lakeside stations, with nighttime levels (1.24 ±4.68) μg·m^-3 higher.No significant differences were found for PM_2.5 concentrations.Using a two-dimensional land surface model, we conducted sensitivity experiments to examine the effects of lake presence and lake-to-urban land distribution under different emission scenarios.Simulations indicated that the model accurately reproduced key temperature and pollutant mass concentrations patterns, comparable to more complex mesoscale model results.Thermal property differences between lake and urban land surfaces significantly impacted low-level atmospheric circulation and vertical stability, altering pollutant diffusion and transport.Daytime thermal stability and limited vertical diffusion over lakeside areas led to a higher concentrations of surface-emitted pollutants near lakes, while concentrations of pollutants formed at mid-levels were lower compared to non-lakeside areas;this pattern reversed at night.Simulation outcomes aligned well with observed data trends and were qualitatively consistent with WRF-Chem results.While emphasizing rigorous monitoring and data processing methods, spatial heterogeneity of urban structures and emissions, as well as observational data limitations, introduced some uncertainties.Future research should incorporate more extensive data from diverse urban regions to better generalize these patterns and strengthen the theoretical foundation for air quality management in urban lakeside environments.