城市交叉路口车辆排放颗粒物浓度的时间相关性分析

Time-correlation Analysis of Particulate Matters from Vehicular Emissions at Urban Traffic Intersection

关键词:  颗粒物  相关性分析  功率谱  交叉路口

Key words:  particulate matter  correlation analysis  power spectrum  intersection

摘要:

[目的]研究大都市道路交叉口车辆尾气排放的颗粒物对大气质量的影响.[方法]在香港街谷一个典型的道路交叉口处,测量不同日期交通高峰时段内车辆排放的6种不同粒径(0.03~0.49 μm,0.5~0.99 μm,1~1.99 μm,2~4.99 μm,5~9.99 μm, ≥ 10 μm)的颗粒物浓度,并通过自相关特性和功率谱分析对这些颗粒物浓度的时间相关性进行分析.[结果]粒径0.03~0.49 μm颗粒物的相关性变化呈现多周期性.与此相反,粒径0.5~0.99 μm,1~1.99 μm和2~4.99 μm颗粒物的相关性明显呈现出与交通红绿灯匹配的周期性,粒径5.0~9.99 μm和 ≥ 10 μm较大颗粒物的相关性较小.粒径较小颗粒物的长时间相关函数不趋于0表明存在长时持续作用.功率谱的分析进一步证实了这6种不同粒径的颗粒物浓度的周期性和长时持续性,特别是粒径0.03~0.49 μm细微颗粒物,其功率谱呈现S(f_k)~1/f_k^η的标度关系,表明存在长时相关特性.[结论]城市道路交叉口车辆尾气排放的颗粒物对大气有较大的影响,6种不同粒径的颗粒物浓度显示出周期性和长时相关持续性。

Abstract:

[Objective] In the paper, we study the effects of particulate matters emitted (0.03~0.49 μm, 0.5~0.99 μm, 1~1.99 μm, 2~4.99 μm, 5~9.99 μm, ≥ 10 μm from vehicles at intersection of urban on air quality.[Methods] Six particulate matters from vehicle emissions at a typical traffic intersection of street canyon in Hong Kong were measured and collected in rush hour on different date, respectively. The time correlation analyses were performed through autocorrelation and power spectrum.[Results] The correlative variation of particulate matters with the grain diameter 0.03~0.49 μm does not reveal obvious unified periodicity, but multiplex periodicity.On the contrary, correlation of particulate matters with the grain diameter 0.5~0.99 μm, 1~1.99 μm and 2~4.99 μm emerge periodicities approximately matching with traffic light periods.For particulate matter with large the grain diameter like 5.0~9.99 μm and ≥ 10 μm, their correlations are small and change quickly.Nonzero value of correlated variations with time implies long-term persistence of tiny particulate matter from emissions.Periodogram in power spectrum analyses further illustrates that evolutions of six particulate matters from vehicle emissions have oscillating periodicities and long-term trend on different date.Especial to the ultrafine particulate matters with grain diameter 0.03~0.49 μm, it shows periodicity without the unified period on different date.Scaling relation of power spectrum for particulate matters indicates the existence of long-term correlation.[Conclusion] Particulate matters from vehicles emission have a great influence on air quality at intersection of urban.Six kinds of particulate matters with the different grain diameter from vehicle emissions reveal periodicities and long-term trend.