Fast response measurements of the dispersion of nanoparticles in a vehicle wake and a street canyon
Fast response measurements of the dispersion of nanoparticles in a vehicle wake and a street canyon
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DOI：
10.1016/j.atmosenv.2009.08.042
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发表时间：
2009-12-01
影响因子：
5
通讯作者：
Britter, Rex
中科院分区：
文献类型：
--
作者：
Kumar, Prashant;Robins, Alan;Britter, Rex
在车辆尾气排放过程中，由于相变过程的影响，直径小于300 nm的纳米颗粒的分布发生了很大的变化。这一时间尺度上的信息对于纳米粒子扩散的模型很重要，但由于现有仪器的采样频率无法捕捉到这些快速过程，因此尚不清楚。在这项研究中，一台最初设计用于测量发动机尾气中颗粒物数量分布(PND)和浓度的快速响应差分迁移率光谱仪(燃烧仪器DMS500)被部署在10赫兹的采样频率下测量5-1000 nm尺寸范围的颗粒物。本文介绍了两项独立研究的结果：一项是沿剑桥(英国)街道峡谷的路边进行的测量，另一项是在固定位置(高于道路水平20厘米)进行的测量，中心位置是一辆柴油发动机汽车行驶后的测量结果。第一次测量的目的是测试DMS500对环境测量的适宜性并推荐最佳操作条件。第二项研究的目的是调查稀释和转化过程(成核、冷凝和凝聚)的相互影响在多长时间内对汽车行驶后的PND产生影响。结果表明，由于尾流中的快速稀释，在排放后约1 S内，转化过程的影响基本完成。此外，街道峡谷的路边测量表明，在风平浪静的情况下，交通排放到达路边的时间约为456 S，这表明当在路边观察到颗粒时，转化过程的影响通常已经完成，因此可以假设总颗粒物数量是守恒的。这一假设的一个推论是，一旦非常接近排气的过程完成，在对街道峡谷中纳米颗粒的行为进行建模时，可以忽略复杂的转化过程。(C)2009爱思唯尔有限公司。保留所有权利。
The distributions of nanoparticles (below 300 nm in diameter) change rapidly after emission from the tail pipe of a moving vehicle due to the influence of transformation processes. information on this time scale is important for modelling of nanoparticle dispersion but is unknown because the sampling frequencies of available instruments are unable to capture these rapid processes. In this study, a fast response differential mobility spectrometer (Cambustion Instruments DMS500), originally designed to measure particle number distributions (PNDs) and concentrations in engine exhaust emissions, was deployed to measure particles in the 5-1000 nm size range at a sampling frequency of 10 Hz. This article presents results of two separate studies: one, measurements along the roadside in a Cambridge (UK) street canyon and, two, measurements at a fixed position (20 cm above road level), centrally, in the wake of a single moving diesel-engined car. The aims of the first measurements were to test the suitability and recommend optimum operating conditions of the DMS500 for ambient measurements. The aim of the second study was to investigate the time scale over which competing influences of dilution and transformation processes (nucleation, condensation and coagulation) affect the PNDs in the wake of a moving car. Results suggested that the effect of transformation processes was nearly complete within about 1 s after emission due to rapid dilution in the vehicle wake. Furthermore, roadside measurements in a street canyon showed that the time for traffic emissions to reach the roadside in calm wind conditions was about 45 6 s. These observations suggest the hypothesis that the effects of transformation processes are generally complete by the time particles are observed at roadside and the total particle numbers can then be assumed as conserved. A corollary of this hypothesis is that complex transformation processes can be ignored when modelling the behaviour of nanoparticles in street canyons once the very near-exhaust processes are complete. (C) 2009 Elsevier Ltd. All rights reserved.