Tehran, the capital of Iran, is one of the most polluted cities in the Middle East. However, there is no clear evidence of the effects of Tehran green spaces on reducing air pollution because there are still challenges to application of vegetation for improving air quality. The current study investigates the effects of a large volume of green space with 275 ha area in the vicinity of major highways on nearby air quality. Similar environments are often seen in many cities around the world. A computational fluid dynamics model containing aerodynamics and deposition effects of vegetation was used to simulate pollutant dispersion for eight wind directions and three different foliage densities. Analysis of results showed that the existence of trees in the green space reduces averaged concentrations of pollutants, including PM₁₀, CO, NO_x, and VOC over the studied site at pedestrian level. The best improvement of air quality was achieved on PM₁₀ with 9% and 8% reductions for the scenarios without and with background concentration, respectively. In addition, the aerodynamics effect of vegetation was dominant for all pollutants in the scenarios without background concentration, while the deposition effect of vegetation was more important for PM₁₀ and VOC in the scenarios with background concentration due to effects of deposition velocities. By increasing leaf area density, small variations of aerodynamic effect were observed, but deposition effects for PM₁₀ and VOC were significantly intensified. Wind directions of 135^o and 315^o, which air easily flows within the domain, maximized the performance of park vegetation. PM₁₀ deposition on tree leaves during dust storm also reduced its concentration by a maximum of 7%. Furthermore, it was found that biogenic VOC emission from trees in the park was not comparable with road emissions at city scale since it increased VOC concentration up to a maximum of 3%.

德黑兰是伊朗的首都，是中东污染最严重的城市之一。但是，尚无德黑兰绿色空间对减少空气污染的影响的明确证据，因为应用植被改善空气质量仍然存在挑战。当前的研究调查了主要高速公路附近275公顷面积的大量绿地对附近空气质量的影响。在世界上许多城市中经常看到类似的环境。使用包含空气动力学和植被沉积效应的计算流体动力学模型来模拟八个风向和三种不同树叶密度下的污染物扩散。结果分析表明，绿地中树木的存在降低了包括PM ₁₀在内的污染物的平均浓度，研究对象在行人层面的CO，NO _x和VOC含量。在没有背景浓度和有背景浓度的情况下，PM ₁₀的空气质量得到了最佳改善，分别降低了9％和8％。此外，在没有背景浓度的情况下，植被的空气动力学效应在所有污染物中均占主导地位，而在背景浓度的情况下，由于沉积速度的影响，植被的沉积作用对PM ₁₀和VOC更为重要。通过增加叶面积密度，可以观察到空气动力学效应的微小变化，但PM ₁₀和VOC的沉积效应显着增强。风向135 ^o和315^o空气易于在区域内流动，从而最大化了公园植被的性能。在沙尘暴期间，PM ₁₀沉积在树叶上的浓度也最多降低了7％。此外，还发现公园树木的挥发性有机化合物排放量与城市道路排放量不具有可比性，因为它使挥发性有机化合物的浓度最高增加了3％。