Based on the ozone mass concentration data in Ningxia from 2015 to 2018, the variations of O3 mass concentration in five cities of Ningxia were analyzed and compared, and the influences of airflow on O3 mass concentration in five cities of Ningxia were discussed by using back trajectory cluster analysis method and the global data assimilation system. The results show that the 90% quantile of O3 mass concentration in Shizuishan was the highest (159 μg·m-3), followed by Yinchuan (154 μg·m-3), Zhongwei (149 μg·m-3), Wuzhong (137 μg·m-3), and Guyuan (132 μg·m-3) during 2015-2018. In the past four years, the O3 mass concentration in Shizuishan decreased slightly, while that in other four cities increased. The days on which  primary pollutants was O3 was 124 days in Shizuishan, 119 days in Zhongwei and 103 days in Yinchuan. The days on which primary pollutants was O3 and air quality was good and  light pollution increased in all 5 cities. Except for Guyuan, the frequency of O3 pullution processes with 6 d and 7 d  duration increased in other cities, especially in Yinchuan and Zhongwei. For Shizuishan, Yinchuan and Wuzhong, the middle-distance and short-distance northwest airflow accounted for the highest percentage of the total airflow trajectory, followed by the southeast airflow and the north airflow. For Zhongwei and Guyuan,the percentage of the southeast airflow  was the highest, followed by the short-distance northwest airflow, and then the middle-distance and long-distance northwest airflow. The northern airflow from central Mongolia, central and western Inner Mongolia, across the northern and central Ningxia was the most important transport path affecting the O3 mass concentration, while the southeastern airflow from south central Shaanxi, northeastern Gansu and middle east Ningxia was the most important transport path affecting the ozone mass concentration in Shizuishan, Yinchuan, Wuzhong and Zhongwei.

Based on the database collected from meteorology observations, transportation system and social economy including 14 evaluation indicators such as gale days with different grades, traffic flow, road density, topographic height, river network density, number of bridge and culvert, bridge and culvert density, vegetation coverage, an expressway gale disaster assessing model was built up to assess the risk of gale disaster along the expressways in Ningxia Province from three aspects including risk of disaster-causing factors, environment sensitivity to gale disaster and vulnerability of gale disaster-bearing body. Then the weight of each influencing indicator was calculated by using the fuzzy comprehensive evaluation method and analytic hierarchy process in order to conduct evaluation of gale disaster risk on expressways in Ningxia. The results indicate that the higher risk areas of gale disaster along expressways in Ningxia Province were mainly located in north section of Shizuishan and south section of Wuzhong, while the risk was lower in the north central and southern part in Ningxia Province. The northern parts of Shizuishan section of G6 (Beijing-Tibet expressway) suffered the high risk of gale disaster, followed by the middle part of Shizuishan section of G6, southern part of Zhongwei plus Wuzhong section of Fuzhou-Yinchuan expressway, while other sections bored medium and low risk of gale disaster. The results of risk assessment were in good agreement with the actual occurrence of gale disasters on expressways.