The Impact of Volatile Organic Compounds and Oxides of Nitrogen on Ground-Level Ozone and Secondary Organic Aerosols Formation Over the Triad Region in North Carolina

Ground-level ozone and secondary organic aerosol (SOA) formation in urban-rural environments involves complex interactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). This study employed WRF-Chem version 4.2 with SAPRC99 chemistry to investigate ozone and SOA formation in the Triad region NC during peak photochemical conditions (1–15 June 2013). Sensitivity simulations examined the impacts of NOx (±20%), anthropogenic VOCs (±20%, −80%), and biogenic emission removal across urban centers (Greensboro, Winston-Salem, High Point) and rural areas (Ellisboro) using nested domains at 12 and 4 km grid spacing. VOC/NOx ratios consistently exceeded 5:1 throughout the region, confirming NOx-limited ozone formation conditions. Ozone showed substantial sensitivity to NOx perturbations (6.5%–8.0% response to ±20% changes) but minimal response to anthropogenic VOC modifications. Biogenic VOC removal reduced ozone by 5.0%–7.6%, with urban areas showing slightly stronger responses. Biogenic SOA contributed ∼60%, while anthropogenic SOA contributed ∼40% of the total SOA mass. Within the biogenic SOA component, isoprene-derived aerosols dominate, accounting for approximately 65% of the total biogenic SOA, while oxidation products of monoterpenes and sesquiterpenes contribute the remaining ∼35%. Reducing anthropogenic VOC emissions by 80% decreased SOA by 18%–22% across all sites. High biogenic VOC emissions deplete oxidant radicals, limiting SOA formation. Removing biogenic emissions enhances anthropogenic SOA by 37%–44% and raises sulfate by 7%, highlighting oxidant competition as a key control. These findings indicate that NOx control measures effectively reduce ozone in the region. SOA management requires balanced approaches targeting both NOx and anthropogenic VOCs due to complex precursor interactions and oxidant competition effects.