激光雷达在城市交通污染中应用研究

机动车排放造成的城市空气污染是目前亟待解决的问题之一。为了分析机动车排放对北京市大气污染的影响,于2007年8月在北京市健翔桥附近利用米氏(Mie)散射激光雷达,对交通排放的颗粒物进行了长时间连续立体监测。实验选取2007年8月16日至21日机动车限行前后的典型数据进行分析,对激光雷达系统及其数据处理方法进行讨论,反演了近地面层颗粒物质量浓度,与车流量和黑炭浓度进行了比对分析。把机动车限行期间与限车前后的观测数据分析比较,发现颗粒物质量浓度与车流量具有很好的相关性,限车期间颗粒物质量浓度总体上呈现下降趋势,证明了机动车限行减排是一项减轻城市大气污染的有效措施。     

北京限行期间大气污染物的差分光学吸收光谱监测与分析

利用差分光学吸收光谱技术于2007年8月对北京市朝阳区大气污染物进行了实时监测,对大气中重要常规污染物NO2、SO2和O3的日变化特征、与天气条件之间的关系和各污染源进行了分析和探讨.通过分析污染物在"好运北京"奥运限车期间(8月17～20日 )与限车前后(8月16、21日)的浓度变化,对机动车限行效果进行了讨论.结果表明,监测点NO2主要来源于汽车尾气,以凌晨和上午时段污染最重,并对O3的来源有着一定的贡献;SO2主要来源于西南方向的污染源,较强风速时北风有利于其浓度的降低;结果还显示机动车限行可有效降低NO2 、SO2浓度,分别达到28.34%和25.87%;但是因导致O3被消耗量降低,致使O3浓度上升.     

北京城区限车期间气溶胶特征激光雷达观测研究

用微脉冲激光雷达(MPL)研究了机动车限行措施对城市大气污染影响.2007年8月北京市车辆限行期间, 对近地面层气溶胶的光学特性进行连续立体监测, 在对激光雷达系统及其数据处理方法讨论的基础上, 反演了近地面层气溶胶消光系数、大气边界层高度以及颗粒物质量浓度的时空变化, 通过和未限车期间近似气象条件下观测数据的分析比较, 发现限车期间颗粒物质量浓度呈现下降趋势, 监测区域上空大气污染层厚度减小, 证明车辆限行减排是一项减轻城市大气污染的有效措施, 为我国城市空气污染治理提供了科学依据和参考.     

北京限行期间大气污染物的DOAS监测与分析

摘要：利用差分光学吸收光谱（DOAS）技术于2007年8月对北京市朝阳区大气污染物进行了实时监测,对大气中重要常规污染物NO2、SO2和O3的日变化特征、与天气条件之间的关系和各污染源进行了分析和探讨。通过分析污染物在“好运北京”奥运限车期间（8月17～20日 ）与限车前后（8月16、21日）的浓度变化,对机动车限行效果进行了讨论。结果表明,监测点NO2主要来源于汽车尾气,以凌晨和上午时段污染最重,并对O3的来源有着一定的贡献;SO2主要来源于西南方向的污染源,较强风速时北风有利于其浓度的降低;结果还显示机动车限行可有效降低NO2 、SO2浓度,分别达到28.34％和25.87％;但是因导致O3被消耗量降低,致使O3浓度上升。     

被动多轴DOAS技术污染气体垂直柱浓度反演方法研究

介绍了基于太阳散射光的多轴被动差分吸收光谱技术与系统及其在大气污染气体垂直柱浓度监测中的应用.实验中利用夫琅和费光谱作为参考光谱,同时将Ring光谱作为一种吸收结构参与拟合去除太阳光谱中的夫琅和费结构和Ring效应对测量结果的影响,并结合辐射传输模型将污染气体斜柱浓度转换为垂直柱浓度,通过“好运北京”奥运限车期间与OMI卫星的对比实验一致得出限车期间NO2有约20％的下降,证实了本方法的可行性.     

生物油催化裂解转化制取三苯

通过不同孔特征的分子筛(HZSM-5、HY沸石和MCM-41)实现生物油催化转化为三苯(苯、甲苯和对甲苯). 基于三苯的产率和选择性,芳香化合物逐次降低顺序为: HZSM-5>MCM-41>HY沸石.用HZSM-5催化裂解生物油产生芳香化合物的最大产率为33.1%,选择性为86.4%. 研究了反应条件对生物油催化裂解的影响,结合催化剂表征结果,讨论了催化剂的结构与性能之间的关系.     

天山北坡绿洲城市车流量与对流层NO2垂直柱浓度关系研究

为探讨天山北坡河谷绿洲城市车流量与对流层NO₂垂直柱浓度（VCD）的关系,基于各城市车流量状况,利用地基多轴差分光谱仪（Mini MAX-DOAS）在2018年-2019年天山北坡经济带上的综合性大城市乌鲁木齐、工业型中等城市石河子和工业型小城市阜康市中心区连续固定监测,并沿城市交通主干道进行车载移动监测,研究车流量对NO₂VCD的影响,对比分析山盆体系河谷绿洲城市与中东部发达城市污染严重原因的差异。结果表明：（1）天山北坡大中小城市的车流量日均值大城市乌鲁木齐（1 406辆/5 min）远大于中小城市,中等城市石河子（203辆/5 min）和小城市阜康（185辆/5 min）差异并不显著（p＞0.05）,而各类城市NO₂VCD整体差异显著（p＜0.05）,其日变化峰值有所差异,表现为乌鲁木齐（22.613×1015 molec·cm-2）＞阜康（17.758×1015 molec·cm-2）＞石河子（15.272×1015 molec·cm-2）,三类城市的车流量和NO₂VCD的日变化趋势一致,都呈现出“早晚高,中午低”的变化趋势;季节变化中三类城市的车流量和NO₂VCD均为：冬春季＞秋夏季;（2）虽然早晚各监测点的车流量有所差异,但三类城市的车流都集中在市中心附近;移动监测数据表明,NO₂VCD高值出现在车流较高的市区,并且在各城市风向稳定时,下风向浓度大于上风向;由于居住空间差异,人们在城市各功能区间的活动,车辆流向和NO₂VCD都集中于人流密集的商业区,说明车辆对NO₂VCD具有较大贡献;（3）2009年-2019年10年间天山北坡大中小城市经济生产总值增长率在200%以上,乌鲁木齐、石河子机动车增长率超过北京、上海等发达城市,城市快速发展,并处于河谷绿洲地带,地势南高北低,冬季逆温层深厚,静风天数较多,采暖期长达6个月,造成冬季污染严重。天山北坡城市除人为污染排放外,自然因素对污染物形成聚集作用。     

被动多轴DOAS技术污染气体垂直柱浓度反演方法研究

介绍了基于太阳散射光的多轴被动差分吸收光谱技术与系统及其在大气污染气体垂直柱浓度监测中的应用．实验中利用夫琅和费光谱作为参考光谱,同时将Ring光谱作为一种吸收结构参与拟合去除太阳光谱中的夫琅和费结构和Ring效应对测量结果的影响,并结合辐射传输模型将污染气体斜柱浓度转换为垂直柱浓度,通过“好运北京”奥运限车期间与OMI卫星的对比实验一致得出限车期间NO2有约20％的下降,证实了本方法的可行性．     

基于差分吸收光谱技术监测苯-甲苯-二甲苯的实验研究

苯-甲苯-二甲苯(BTX)是大气挥发性有机物(VOCs）的重要组成成份,人类长期暴露在苯系物的环境中致癌风险将极大提高。利用BTX在紫外波段有明显的光谱吸收特征,选取250～275 nm作为研究波段,该波段可将BTX的主要特征吸收包含在内。设计了一套由标准BTX液体制备标准气态BTX的装置,采用连续紫外光源和差分吸收光谱技术分别对单组分苯与BTX混合气体进行连续监测研究。为最大程度去除外界噪声干扰,分别采用小波变换滤波和多项式平滑滤波法,并对两种方法的去噪效果进行评价。研究表明尽管传统处理吸收光谱噪声的方法常采用多项式平滑滤波,但该方法会使吸收截面上的细节信息或高频分量丢失。而小波变换滤波具有良好的时频局域化特性,能通过伸缩和平移对信号进行多分辨率分析并可聚焦到信号的任意细节,更能保持光谱谱线的特征结构且信噪比优于多项式平滑滤波。通过实验获得了BTX的吸收截面并与HITRAN数据库吸收截面对比,发现若直接采用HITRAN数据库中吸收截面值将造成由于温度与压强变化导致的浓度反演误差。为了能够与实际监测环境相符合,采用实验室获取的吸收截面作为标准吸收截面。对单组分苯浓度的反演分别采用积分面积法和最小二乘法,研究表明两种方法的测量精度均能满足环保监测法规要求,且最小二乘法更加稳定、精度更高。针对BTX混合气体的测量,采用通过浓度值反演差分吸光度的方法进而逐一反演苯-甲苯-二甲苯的浓度值。研究发现对BTX混合物的浓度反演时二甲苯测量误差均在2%以下,但对甲苯和苯的测量误差逐渐增大,苯浓度的反演最大误差达到了9.07%,苯的测量精度受到了二甲苯、甲苯测量精度以及苯光谱特征吸收波段的影响。     

用烟雾箱研究甲苯与OH自由基光化学反应

文中用自制的烟雾腔系统研究了甲苯与OH自由基的光化学反应,得到的结论是其在大气中的主要产物是苯醛、甲基苯酚和苯硝酸甲脂.甲苯在烟雾箱内的寿命约为60分钟.     

Effect of signals on two-route traffic system with real-time information

We study the effect of signals on the vehicular traffic in the two-route system at the tour-time feedback strategy where the vehicles move ahead through a series of signals. The Nagel–Schreckenberg model is applied to the vehicular motion. The traffic signals are controlled by both cycle time and split. The tour times on two routes fluctuate periodically and alternately. The period increases with decreasing the split. Also, the tour time on each route varies with time by synchronizing with the density. The dependences of tour times and densities on both split and cycle time are clarified.     

Traffic dispersion induced by noise in off-lattice model

We study the dispersion of vehicles induced by speed fluctuation on a single-lane highway under open boundary. We extend the cellular automaton model on one-dimensional lattice to the real-variable model on off-lattice (continuous-in space model) in order to take into account the fluctuation of vehicular speed. Vehicles extend over the highway when moving forward. The characteristics of traffic dispersion are derived. It is shown that vehicular traffic exhibits scaling property. When a vehicle accelerates for following the vehicle ahead, vehicles move forming a cluster without dispersion. The relationship between the width of vehicular cluster and acceleration rate is clarified.     

Clustering and maximal flow in vehicular traffic through a sequence of traffic lights

We study the maximal current (maximum traffic capacity) of vehicular traffic through a sequence of traffic lights on a highway, where all signals turn on and off synchronously. The dynamical model of vehicular traffic controlled by signals is expressed in terms of a nonlinear map, where the excluded-volume effect is taken into account. The dynamical behaviors of vehicles are clarified by analyzing traffic patterns. The clustering of vehicles varies with the cycle time of signals. The maximum current is closely connected to vehicular clustering. Clustering of vehicles is controlled by varying both split and cycle time of signals. The dependence of the maximal current on both split and cycle time is derived.     

Enskog-like kinetic models for vehicular traffic

In the present paper a general criticism of kinetic equations for vehicular traffic is given. The necessity of introducing an Enskog-type correction into these equations is shown. An Enskog-like kinetic traffic flow equation is presented and fluid dynamic equations are derived. This derivation yields new coefficients for the standard fluid dynamic equations of vehicular traffic. Numerical simulations for inhomogeneous traffic flow situations are shown together with a comparison between kinetic and fluid dynamic models.     

Vehicular motion in 2D city traffic network with signals controlled by phase shift

We study the dynamic behavior of vehicular traffic through the series of traffic lights controlled by phase shift in two-dimensional (2D) city traffic network. The nonlinear-map model is presented for the vehicular traffic. The city traffic network is made of one-way perpendicular streets arranged in a square lattice with traffic signals where vertical streets are oriented upwards and horizontal streets are oriented rightwards. There are two traffic lights for the movement to north or that to east at each crossing. The traffic lights are controlled by the cycle time, split, and phase shift. The vehicle moves through the series of signals on a path selected by the driver. The city traffic with a heterogeneous density distribution is also studied. The dependence of the arrival time on cycle time, split, phase shift, selected path, and density is clarified for 2D city traffic. It is shown that the vehicular traffic is efficiently controlled by the phase shift.     

Phase states of traffic flows in linear tunnels. Analysis of empirical data

The empirical data on traffic flows collected in the linear portion of the Lefortovsky tunnel of the third Moscow transport ring were analyzed. It was shown that the crowded traffic observed in the tunnel is indeed characterized by the synchronized vehicular traffic. In particular, long-range spatial correlations in their motion velocities and the region of “widely scattered states”, i.e., two typical properties of the synchronized vehicular traffic phase, were detected in the fundamental diagram. Moreover, the phase diagram of the traffic flow dynamics showed two regions with essentially different properties, which are separated by a narrow layer with a virtually fixed vehicle density. One of them corresponds to synchronized vehicular traffic and contains a core of chaotic dynamics. Another region corresponds to irreversible formation of wide moving jams.     

Influence of expanding ring roads on traffic noise in Beijing City

The road network in Beijing is expanding in the form of loop-lines. Following the 2nd and 3rd ring roads, the 4th has been completed and come into operation in 2002. Traffic noise surveying and analysis was performed along four main roads in the Beijing urban area—the 2nd, 3rd and 4th ring roads circling the central downtown area and Chang-An Avenue, a major east-west corridor through the heart of the city. Measured noise data along the 2nd, 3rd and Chang-An Avenue were compared with the data surveyed before the completion of the 4th ring road for determining influence of expanding ring roads on traffic noise pattern in Beijing City. The results indicate that these main roads remain overloaded by traffic flow during daytime, and noise levels due to road traffic along these roads exceeds relavent environmental standards by 5 dBA. Reduced traffic noise level was observed along the northern half of the 2nd and 3rd ring roads, and along the central section of Chang-An Avenue. Increased traffic noise level was observed along the southern half of the 2nd and 3rd ring roads, and along the non-central section of Chang-An Avenue. Expanding ring roads mitigate heavy traffic flow in the central part of Beijing City, but spread high traffic noise outwards at the same time.     

Vehicular traffic flow through a series of signals with cycle time generated by a logistic map

We study the dynamical behavior of vehicular traffic through a series of traffic signals. The vehicular traffic is controlled with the use of the cycle time generated by a logistic map. Each signal changes periodically with a cycle time, and the cycle time varies from signal to signal. The nonlinear dynamic model of the vehicular motion is presented by a nonlinear map including the logistic map. The vehicular traffic exhibits very complex behavior on varying both the cycle time and the logistic-map parameter a$a$. For a>3$a>3$, the arrival time shows a linear dependence on the cycle time. Also, the dependence of vehicular motion on parameter a$a$ is clarified.