为研究绿化带对交通噪声的衰减效应,在北京市郊国道边或市区内有代表性的绿化带设置30 m 宽林带23个,测试不同类型林带对实时交通噪声、模拟交通噪声、白噪声和不同频率噪声(125 ~ 8 000 Hz)的降噪值,并分析了季节和距噪声源的距离对各林带降噪效果的影响。结果显示:不同林带的降噪效果有明显差异。对于实时交通噪声,降噪效果最佳的是刺槐(Robinia pseudoacacia)纯林和油松-刺柏(Pinus  tabulaeformis-Juniperus formosana)混交林,最弱的是旱柳(Salix matsudana)纯林;对于模拟交通噪声,降噪效果最佳的是刺柏-侧柏(Juniperus formosana-Platycladus orientalis)混交林和国槐(Sophora japonica)纯林,最弱的是旱柳纯林和加杨(Populus ×canadensis)纯林;对于白噪声,油松纯林的降噪效果较好,银杏-圆柏(Ginkgo biloba-Sabina chinensis)混交林降噪效果较差。冬季不同林带对不同噪声的衰减效果总体上小于夏季,其中,针叶混交林、针阔叶混交林或针叶纯林在夏、冬季对实时交通噪声和模拟交通噪声或白噪声的降噪效果接近。10 m 宽林带的降噪值随距噪声源距离的变化而差异明显,离噪声源越近降噪效果越好。不同林带对中低频率(2 000 Hz 以下)噪声的整体降噪效果优于对高频噪声的降噪效果,其中对500 Hz 噪声的降噪值最大,对5 000 和8 000 Hz 噪声的降噪值最小。为了充分发挥绿化带的降噪功能,根据研究结果,建议在公路绿化带建设中应优先选用针叶混交林或分枝高度较低且分枝多、叶片小而密集的树种;绿化带的宽度至少10 m 且应规则种植。

In order to study attenuation effect of green belt on traffic noise, 23 forest belts with 30 m

width were set up in representative green belts beside national highway in suburb or inside urban area of Beijing City. Noise reduction value of forest belts with different types to real-time traffic noise, simulated traffic noise, white noise and noise with different frequencies (125-8 000 Hz) were determined, and influences of season and distance away from noise sources on noise reduction effect of different forest belts were analyzed. The results show that there is obvious difference in noise reduction effect among different forest belts. For real-time traffic noise, noise reduction effect of pure forest of Robinia pseudoacacia and mixed forest of Pinus tabulaeformis -Juniperus formosana is the best, while that of pure forest of Salix matsudana is the worst. For simulated traffic noise, noise reduction effect of mixed forest of Juniperus formosana-Platycladus orientalis and pure forest of Sophora japonica is the best, while that of pure forest of Salix matsudana and pure forest of Populus ×canadensis is the worst. For white noise, noise reduction effect of pure forest of Pinus tabulaeformis is better, while that of mixed forest of Ginkgo biloba-Sabina chinensis is worse. Attenuation effect of different forest belts on different noises in winter is generally lower than that in summer. In which, noise reduction effect of coniferous mixed forest and coniferous broad-leaved mixed forest or coniferous pure forest on real-time traffic noise and simulated traffic noise or white noise in winter is close to that in summer. Noise reduction value of all forest belts with 10 m width has the obvious difference with changing of distance away from noise sources, and the nearer away from noise sources, the better of noise reduction effect. Noise reduction effect of different forest belts on low-middle frequency (below 2 000 Hz) noise is better than that on high frequency noise, in which, noise reduction value to 500 Hz noise is the highest and that to 5 000 and 8 000 Hz noise is the lowest. In order to play fully noise reduction function of green belts, according to these research results, it is suggested that in construction of road green belts, coniferous mixed forest or some tree species with lower branch height, more branches, and small and dense leaves should be chosen preferentially and planted regularly, and the width of green belts should be 10 m at least.