利用逐时地面气象数据、探空秒级数据及风廓线雷达数据分析了2013—2017年乌鲁木齐低空焚风演变时边界层和近地层气象扩散条件的变化特征。结果表明：（1） 乌鲁木齐大气扩散条件总体呈现夏季最有利,冬季最差（最大混合层厚度0.44×10³ m、通风系数1.52×10³ m²·s^-1、逆温层厚度768 m、逆温层温差4.82 ℃、静稳指数6.36）,且冬季12月与1月极不利于污染物扩散。（2） 冬季低空焚风演变的5个阶段,大气混合层厚度、通风系数呈减小—增大特征,焚风强盛期混合层厚度最低（0.30×10³ m）、通风系数最小（0.62×10³ m²·s^-1）;逆温层厚度及强度、静稳指数变化趋势为增大—减小特征,强盛期逆温最强（10.9 ℃）、逆温层厚度（0.99×10³ m）、静稳指数最大（9.7）。（3） 低空焚风过程的发展期和强盛期各站气压减小,高海拔站点气温升高、风速增大,焚风层以下低海拔区域气温降低、风速减小,说明焚风使得焚风层以下区域的大气更加稳定,不利于污染物扩散。（4） 总体上焚风致使水平扩散能力和垂直交换能力减弱,大气易凝结,结束后扩散条件重建。业务中可利用焚风发展趋势预判边界层扩散条件及地面气象要素的演变,为乌鲁木齐城市群空气污染预报和污染治理提供参考依据。

On the basis of hourly surface meteorological data, radiosonde second-level data, and wind profile radar data collected from 2013 to 2017, the low-level foehn wind and its evolution characteristics in Urumqi City, Xinjiang, China, were identified. According to various calculation parameters and methods in the boundary layer, including mixed layer thickness, inversion layer thickness, ventilation coefficient, and static stability index, the variation of the boundary-layer diffusion conditions in Urumqi City during the evolution of low-level foehn wind were analyzed. The results demonstrated that the atmospheric diffusion conditions in Urumqi City have been most favorable in summer and worst in winter (maximum thickness of the mixed layer=0.44×10³ m; ventilation coefficient=1.52×10³ m²·s^-1; inversion layer thickness=768 m; temperature difference of the inversion layer=4.82 ℃; static stability index=6.36), and December and January were extremely unfavorable in terms of pollutant diffusion. In the five stages of low-level foehn evolution, the thickness of the atmospheric mixing layer and the ventilation coefficient first increased and then decreased, and the value has been the lowest in the vigorous period of foehn development. The thickness, strength, and static stability index of the inversion layer were opposite, and the maximum value occurred in the vigorous period. The air pressure at each station also decreased during the development and the prosperous period of the foehn weather process. The temperature and wind speed of the high-altitude station at the bottom of the foehn increased, whereas those of the low-altitude station decreased, indicating that the foehn made the lower atmosphere more stable and was not conducive to the diffusion of pollutants. Generally, horizontal diffusion capacity and vertical exchange capacity are weakened by foehn, and the atmosphere is easy to condense. For future operations, the foehn development trend can be used to predict diffusion conditions, providing a reference for the air pollution forecast and the control of urban agglomeration in Urumqi City.