Assessing chemistry schemes and constraints in air quality models used to predict ozone in London against the detailed Master Chemical Mechanism

Additional HONO and OH Generation from Photoexcited Phenyl Organic Nitrates in the Photoreaction of Aromatics and NOx

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NOx. Significant HONO (1.56-4.52 ppb) and OH production is observed during the photoreaction of different kinds of aromatics with NOx (18.1-242.3 ppb). We propose an additional mechanism involving photoexcited phenyl organic nitrates (RONO2) reacting with water vapor to account for the higher levels of measured HONO and OH than the model prediction. The proposed HONO formation mechanism was evidenced directly by photolysis experiments using typical RONO2 under UV irradiation conditions, during which HONO formation was enhanced by relative humidity. The 0-D box model incorporated in this mechanism accurately reproduced the evolution of HONO and aromatic. The proposed mechanism contributes 5.9-36.6% of HONO formation as the NOx concentration increased in the photoreaction of aromatics and NOx. Our study implies that photoexcited phenyl organic nitrates are an important source of atmospheric HONO and OH that contributes significantly to atmospheric oxidation capacity.

Implications of Mitigating Ozone and Fine Particulate Matter Pollution in the Guangdong-Hong Kong-Macau Greater Bay Area of China Using a Regional-To-Local Coupling Model

Ultrahigh-resolution air quality models that resolve sharp gradients of pollutant concentrations benefit the assessment of human health impacts. Mitigating fine particulate matter (PM_2.5) concentrations over the past decade has triggered ozone (O₃) deterioration in China. Effective control of both pollutants remains poorly understood from an ultrahigh-resolution perspective. We propose a regional-to-local model suitable for quantitatively mitigating pollution pathways at various resolutions. Sensitivity scenarios for controlling nitrogen oxide (NO_x) and volatile organic compound (VOC) emissions are explored, focusing on traffic and industrial sectors. The results show that concurrent controls on both sectors lead to reductions of 17%, 5%, and 47% in NO_x, PM_2.5, and VOC emissions, respectively. The reduced traffic scenario leads to reduced NO₂ and PM_2.5 but increased O₃ concentrations in urban areas. Guangzhou is located in a VOC-limited O₃ formation regime, and traffic is a key factor in controlling NO_x and O₃. The reduced industrial VOC scenario leads to reduced O₃ concentrations throughout the mitigation domain. The maximum decrease in median hourly NO₂ is >11 μg/m³, and the maximum increase in the median daily maximum 8-hr rolling O₃ is >10 μg/m³ for the reduced traffic scenario. When controls on both sectors are applied, the O₃ increase reduces to <7 μg/m³. The daily averaged PM_2.5 decreases by <2 μg/m³ for the reduced traffic scenario and varies little for the reduced industrial VOC scenario. An O₃ episode analysis of the dual-control scenario leads to O₃ decreases of up to 15 μg/m³ (8-hr metric) and 25 μg/m³ (1-hr metric) in rural areas.