高架街谷中交通污染物的垂直分布和时变特征研究

Vertical distributions and temporal variations of traffic pollutants in elevated street canyons

为探讨交通、气象因素和街谷高宽比对于高架街谷中污染物分布的影响,本研究于中国广州市开展了两期污染物(PM_(1)、PM_(2.5)、PM_(1)0(分别为空气动力学直径小于或等于1、2.5和10μm的颗粒物)、超细颗粒物(UFP)和黑碳(BC))监测实验.结果表明,1期实验(高度不对称街谷)BC、PM_(1)、PM_(2.5)和PM_(1)0的整体浓度分别为(3.0±2.2)、(27±13)、(34±15)和(59±27)μg·m^(-3);2期实验(深窄街谷) BC、PM_(1)、PM_(2.5)和PM_(1)0的整体浓度分别为(2.2±0.7)、(19±5)、(26±6)和(59±21)μg·m^(-3);UFP浓度分别为13.57×10^(3)和18.35×10^(3)个·cm^(-3).1期实验PM_(1)、PM_(2.5)、PM_(1)0和UFP的每日垂直剖面均呈现从地面道路至高架桥处先降低后升高,而后缓慢降低的相似规律,从高架桥至顶端,污染物浓度平均变化了-5.9%、-4.7%、1.4%和-4.8%;由于对车辆排放的高敏感性,BC的每日垂直剖面分布规律无一致性.此外,街谷高宽比通过影响隔音屏障设置和流场分布,进而影响高架桥上方的污染物扩散,改变了污染物的垂直剖面分布.分析污染物时间变化规律,发现颗粒物的小时变化主要归因于交通排放的日变化和大气边界层的综合影响;UFP和BC有着不同于颗粒物的日变化趋势,分别归因于午后光化学反应和道路车辆瞬态排放.进一步分析污染物变化和车流量相关性表明,污染物的日变化特征与交通变化过程联系紧密,且高峰期和交通构成对不同污染物的影响具有差异性.这些发现可为城市交通管控和人群健康改善提供参考.

In order to investigate the effects of traffic,meteorological factors and aspect ratios on the distributions of pollutants in street canyons with viaducts,two phases of experiments with simultaneous monitoring of pollutants(PM_(1),PM_(2.5),PM_(1)0(particulate matter with aerodynamic diameters less than or equal to 1 micron,2.5 microns and 10 microns respectively),ultrafine particulate matter(UFP),and black carbon(BC))and traffic volumes were carried out in street canyons with a viaduct of different aspect ratios in Guangzhou City,China.The results showed that the average concentrations of BC,PM_(1),PM_(2.5) and PM_(1)0 in the first phase of the experiment(highly asymmetric street valley)were(3.0±2.2),(27±13),(34±15)and(59±27)μg·m^(-3),and the average concentrations in the second phase of the experiment(deep street canyon)were(2.2±0.7),(19±5),(26±6)and(59±21)μg·m^(-3),respectively.UFP concentrations were 13.57×103 cm^(-3) and 18.35×103 cm^(-3) in two phases of experiments respectively.The daily vertical profiles of PM_(1),PM_(2.5),PM_(1)0 and UFP in the first phase were all presented similar patterns,which first decreased,then increased and then slowly decreased from the surface road to the viaduct.From the viaduct to the top one of the sampling locations,the pollutant concentration changed on average by-5.9%,-4.7%,1.4%and-4.8%.Due to the high sensitivity to vehicle emissions,the daily vertical profile distribution pattern of BC was inconsistent.In addition,the aspect ratios of street canyon affected the dispersion of pollutants above the viaduct by influencing the setting of noise barriers and flow field distributions,leading to the changing of the vertical profiles of pollutants.Analysis of the temporal variations of pollutants,it was found that the hourly variations of PMs were mainly attributed to the combined influence of the diurnal variation of traffic emissions and atmospheric boundary layer.The diurnal variations of UFP and BC showed different trends from those of PMs, which were mainly caused by the photochemical reactions in the afternoon and transient emissions from on-road vehicles, respectively. Further analysis of the correlations between pollutants and traffic flow showed that the diurnal variations of pollutants were closely related to the traffic processes, and the impacts of peak periods and traffic compositions on different pollutants showed discrepancies. These findings can provide guidance for urban traffic control and provide reference for improving public health.