Sub-seasonal and Spatial Variations in Ozone Formation and Co-control Potential for Secondary Aerosols in the Guanzhong Basin, Central China

Abstract. Tropospheric ozone (O₃) pollution in warm seasons has become the key air-quality issue in the Guanzhong Basin (GZB), threatening human health despite prior successes in particulate matter control. Understanding how O₃ formation regimes (OFR) and secondary aerosol (SA) formation regimes (SAFR) evolve with time and space is critical for designing coordinated control strategies. Long-term near-surface observations (2014–2024) are combined with high-resolution WRF-Chem simulations for May–August 2022, employing scenario-based EKMA curves and source-apportionment diagnostics to resolve sectoral contributions. Results indicate a sub-seasonal OFR progression from VOCs-limited in early summer to transitional in midsummer and NO_X-limited in late summer, with anthropogenic contribution to the maximum daily averaged 8-h (MDA8) O₃ increasing from 32.8 % in May to 55.2 % in July and biogenic share peaking 18.7 % in July. SAFR follows a distinct cycle with NO_X-limited in May, VOCs-limited in June, and transitional behavior thereafter. Traffic and industrial emissions are the dominate anthropogenic divers for both O₃ and SA. These patterns highlight phases of synergistic control, where anthropogenic VOCs mitigation in June and NO_X mitigation in August maximize co-benefits while minimizing trade-offs. This study integrated dynamic OFR/SAFR diagnostics with sectoral emission inventories can provide insights into pathways toward seasonally adaptive, city-specific air quality management in the GZB.