Influence of Refined Soil NO Emissions on Summertime Ozone Modeling and Mitigation Efficacy: A Case Study in China

Abstract

Tropospheric ozone (O3) pollution during summertime has emerged as a major environmental challenge in China. While anthropogenic NOx controls are being aggressively implemented, the influence of biogenic sources, particularly soil NO emissions during peak agricultural periods, remains a critical uncertainty in air quality modeling. This study investigates the influence of refined soil NO emissions on O3 simulation during a representative summertime period (June 2020). By integrating updated environmental response functions, high-resolution fertilizer data, and corrected cropland emission factors into a modified Berkeley–Dalhousie Soil NO Parameterization (BDSNP) scheme, we developed a refined soil NO inventory that leads to a total soil NO estimate of 1.15 Tg N for 2020. Evaluation against 16 in situ flux observations shows a significant reduction in normalized mean bias (NMB, from −38% to −14%). Our numerical simulations reveal that soil NO contributes approximately 15%∼22% to NO2 and 6%∼14% to the population-weighted MDA8 O3 in major urban agglomerations during the simulation period. More importantly, we find that although the overall model bias for surface O3 shows limited statistical improvement, the refined inventory substantially alters the model’s sensitivity to anthropogenic emission controls. A 40% reduction in anthropogenic NOx yields a much smaller O3 benefit (2.5 ppb) compared to the original scheme (4.5 ppb), suggesting that underestimating summertime soil NO may lead to overoptimistic projections of anthropogenic mitigation efficacy during peak pollution months. This case study highlights the necessity of accounting for agricultural nitrogen management in designing effective O3 control strategies.