As the most important urban agglomeration in Northwestern China, the ozone pollution in Guanzhong region has gradually become a prominent problem affecting local air quality in recent years. It is of great significance to explore its spatio-temporal variation characteristics and influencing factors for the atmospheric environment management in this region. Based on hourly mass concentration data of ozone from state-controlled environmental monitoring stations and hourly meteorological data from national meteorological stations in five cities of Guanzhong region from 2014 to 2020, the characteristics of near-ground ozone pollution and its meteorological influencing factors were analyzed comparatively. The results are as follows: (1) The ozone had gradually replaced PM₁₀ as the primary air pollutant after PM_2.5 in Guanzhong region in recent 7 years, and the proportion of days with ozone as the primary pollutant had a fluctuant increasing trend in the whole. (2) The monthly distributions of ozone mass concentration in five cities of Guanzhong region appeared a typical single-peak pattern, the ozone mass concentration was higher in summer (from June to August), and the value of concentration in Xi’an, Xianyang, Weinan, Tongchuan and Baoji decreased in order. The diurnal variations of ozone mass concentration also showed a single-peak pattern, with the trough from 07:00 to 08:00 and the peak from 15:00 to 16:00 in five cities of Guanzhong region. (3) When the maximum temperature is higher than 36 ℃, relative humidity is between 45% and 70% and the average wind speed is between 2 and 3 m·s^-1, the ozone is easy to exceed the standard in Guanzhong region, and the higher maximum temperature is, the greater exceeding standard rate of ozone is. The favorable wind direction to ozone pollution in Xi’an, Tongchuan, Xianyang and Weinan is NE, while that in Baoji is SE or NW. (4) The easterly route from the central and western parts of Henan Province is the most important transport route affecting ozone concentration in summer in Xi’an City. Except for neighbour cities of Shaanxi Province, the central and western Henan Province, Yuncheng of Shanxi Province and the northern Hubei Province are also major potential sources of O₃ pollution in Xi’an City.

In order to get a deeper understanding of the water vapor characteristics and sources of rainstorms in semi-arid areas in Northwest China, and improve the ability of rainstorm forecasting in this area, based on upper-air and surface observation data and European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation global atmospheric reanalysis (ERA5) (0.25 × 0.25),the characteristics of water vapor transport and budget of two large-scale rainstorm processes with different intensities occurring in northern Shaanxi under different circulation on July 11 and August 9, 2022 were analyzed. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to quantitatively analyze the source and contribution rate of water vapor. The results show that the high level trough, low level shear line and vortex and low level jet were the main influence systems of the rainstorm occurring on July 11. 700 hPa cyclonic convergence and 850 hPa low vortex strengthened and moved slowly, causing regional rainstorms. The short-wave trough and low-level shear line were the main influence systems of the rainstorm process on August 9, and the secondary circulation on both sides of the shear line lifted the warm and humid air flow outside the West Pacific Subtropical High (referred to as "West Pacific Sub-high") triggering the release of unstable energy and forming a large-scale convective rainstorm weather. On July 11, the vertically integrated water vapor fluxes from ground to 300 hPa was stronger, 700 hPa southwest jet and the 850 hPa southeast jet formed two obvious water vapor transport belts. The strong convergence lasted longer, the wet layer was deep and the weather process was dominated by stable precipitation. On August 9, under the control of subtropical high, the atmosphere over northern Shaanxi had high temperature and humidity, and the total amount of precipitable water was large. The water vapor transport was weak and the strong convergence maintenance time was short, the wet layer was thinner, but the energy was sufficient, the weather process was dominated by convective precipitation. On July 11, the water vapor net income mainly came from the ground to 500 hPa, of which accounted for 52% during 800-500 hPa. The water vapor income of the eastern boundary below 800 hPa increased rapidly during the precipitation intensification stage and the combination of increased zonal income and strong meridional income keeps the regional net income at a high value, resulting in regional heavy rain. On August 9, almost all of the water vapor net income came from meridional income, and the water vapor net income mainly came from the ground to 800 hPa (accounting for 88%). The 700 hPa shear line moving southward and the convergence in the north of Yulin increased, reduced the outflow of the southerly wind, significantly increased the meridional income of water vapor, and strengthens the rainstorm. Water vapor backward trajectories with HYSPLIT model showed that on July 11, water vapor mainly came from tropical oceans, and the South China Sea contributed the most, the local and surrounding near surface atmosphere with high specific humidity also contributed significantly. On August 9, the water vapor mainly came from the high specific humidity atmosphere in the near-surface layer of the inland, followed by the South China Sea.