Li X L, Wang J S, Tu X D, Liu W, Huang Z
Center for Combustion and Environmental Technology, Shanghai Jiao Tong University, Shanghai, 200030, China.
Sci Total Environ. 2007 Jun 1;378(3):306-16. doi: 10.1016/j.scitotenv.2007.02.040. Epub 2007 Apr 5.
Measurements of particle number size distribution in the range of 10-487 nm were made at four heights on one side of an asymmetric street canyon on Beijing East Road in Shanghai, China. The result showed that the number size distributions were bimodal or trimodal and lognormal in form. Within a certain height from 1.5 to 20 m, the particle size distributions significantly changed with increasing height. The particle number concentrations in the nucleation mode and in the Aitken mode significantly dropped, and the peaking diameter in the Aitken mode shifted to larger sizes. The variations of the particle number size distributions in the accumulation mode were less significant than those in the nucleation and Aitken modes. The particle number size distributions slightly changed with increasing height ranging from 20 to 38 m. The particle number concentrations in the street canyon showed a stronger association with the pre-existing particle concentrations and the intensity of the solar radiation when the traffic flow was stable. The particle number concentrations were observed higher in Test I than in Test II, probably because the small pre-existing particle concentrations and the intense solar radiation promoted the formation of new particles. The pollutant concentrations in the street canyon showed a stronger association with wind speed and direction. For example, the concentrations of total particle surface area, total particle volume, PM2.5 and CO were lower in Test I (high wind speed and step-up canyon) than in Test II (low wind speed and wind blowing parallel to the canyon). The equations for the normalized concentration curves of the total particle number, CO and PM2.5 in Test I and Test II were derived. A power functions was found to be a good estimator for predicting the concentrations of total particle number, CO and PM2.5 at different heights. The decay rates of PM2.5 and CO concentrations were lower in Test I than in Test II. However, the decay rate of the total particle number concentration in Test I was similar to that in Test II. No matter how the wind direction changed, for example, in the step-up case or wind blowing parallel to the canyon, the decay rates of the total particle number concentration were larger than those of PM2.5 and CO concentrations. For example, CO concentrations decreased by 0.33 and 0.69 at the heights ranging from 1.5 to 38 m in Test I and Test II, while the total particle number concentrations decreased by 0.72 and 0.85 within the same height ranges in Test I and Test II. It is concluded that the coagulation process, besides the dilution process, affected the total particle number concentration.
在中国上海北京东路一条不对称街道峡谷一侧的四个高度处，对粒径范围在10 - 487纳米的颗粒物数量粒径分布进行了测量。结果表明，数量粒径分布呈双峰或三峰形态，且符合对数正态分布。在1.5至20米的一定高度范围内，粒径分布随高度增加而显著变化。成核模态和艾肯模态中的颗粒物数量浓度显著下降，艾肯模态中的峰值直径向更大尺寸偏移。积聚模态中颗粒物数量粒径分布的变化不如成核模态和艾肯模态中的显著。在20至38米的高度范围内，颗粒物数量粒径分布随高度增加变化较小。当交通流量稳定时，街道峡谷中的颗粒物数量浓度与先前存在的颗粒物浓度以及太阳辐射强度呈现更强的相关性。在实验一中观测到的颗粒物数量浓度高于实验二，这可能是因为先前存在的颗粒物浓度较低以及太阳辐射强烈促进了新颗粒物的形成。街道峡谷中的污染物浓度与风速和风向呈现更强的相关性。例如，实验一（高风速和阶梯状峡谷）中总颗粒物表面积、总颗粒物体积、PM2.5和CO的浓度低于实验二（低风速且风平行于峡谷吹拂）。推导了实验一和实验二中总颗粒物数量、CO和PM2.5的归一化浓度曲线方程。发现幂函数是预测不同高度处总颗粒物数量、CO和PM2.5浓度的良好估计器。实验一中PM2.5和CO浓度的衰减率低于实验二。然而，实验一中总颗粒物数量浓度的衰减率与实验二相似。无论风向如何变化，例如在阶梯状情形或风平行于峡谷吹拂时，总颗粒物数量浓度的衰减率都大于PM2.5和CO浓度的衰减率。例如，在实验一和实验二中，在1.5至38米的高度范围内，CO浓度分别下降了0.33和0.69，而总颗粒物数量浓度在相同高度范围内分别下降了0.72和0.85。得出的结论是，除稀释过程外，凝聚过程也影响了总颗粒物数量浓度。
