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 NOX-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 NOX-limited in May, VOCs-limited in June, and transitional behavior thereafter. Traffic and industrial emissions are the dominant anthropogenic divers for both O3 and SA. These patterns highlight phases of synergistic control, where anthropogenic VOCs mitigation in June and NOX 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.