Quantitative Evaluation of Meteorological Impacts on Ozone Pollution in Five Cities of China’s Guanzhong Region: Implications for Regional Ozone Pollution Control

Ozone (O3) pollution has become an important constraint on air quality improvement in the Guanzhong region, a typical semi-enclosed terrain in inland China. Based on hourly air quality and meteorological observations during 2019–2023 across five key cities in the Guanzhong region, this study investigated spatiotemporal patterns of O3 and its response to meteorological drivers using correlation analysis, a Meteorology Synthetic Index (MSI), and a vector wind decomposition method for identifying mountain-valley-breeze days. Results showed that regional annual O3 concentrations exhibited an overall upward trend, with monthly peaks in June–July and hourly peaks between 14:00 and 17:00 China Standard Time (UTC + 08:00). Notably, the night-time O3 increase was approximately four times that in daytime, indicating a prominent nocturnal accumulation effect. Spatially, O3 levels were lower in the west and higher in the southeast, with Xi’an and Xianyang as persistent hotspots. Ozone-exceedance days are frequently observed under meteorological conditions of T > 30 °C, RH < 50%, and wind speed < 4 m·s−1 in Guanzhong region. Meteorological factors explained 35% of the MDA8 O3 variance on normal days, which decreased to 4% during moderate-severe pollution episodes. Mountain-valley-breeze days accounted for 43% of the total, with MDA8 O3 levels 12.6 ± 5.7 μg·m−3 higher than that on non-breeze days. This discrepancy was most pronounced during the daytime valley breeze phase and was further intensified during moderate–severe pollution events. The differentiated diurnal ozone amplification effect of valley breeze further supplements global knowledge of terrain-induced ozone stagnation, delivering hierarchical, cross-regional collaborative control guidance for ozone abatement in comparable basin regions across Asia, North America and Europe.