Evaluating near-field effects of large point source emissions on ambient ozone with coupled Lagrangian and Eulerian models.

Understanding and managing the near-field impacts of large point sources (LPSs) on ozone (O3) pollution is critical for effective urban air quality control. This study integrated a Lagrangian-Eulerian modeling framework that combines the Second-Order Closure Integrated Puff with chemistry (SCICHEM) model and the Community Multiscale Air Quality (CMAQ) model (referred to as SCICHEM-CMAQ), to quantify O3 responses to nitrogen oxides (NOx) emissions from cement and power plants, with support from Continuous Emission Monitoring System (CEMS) data. Results revealed that both source types exhibit pronounced peak impacts during late morning to early afternoon hours (10:00-14:00), coinciding with intensified photochemical activity. For instance, peak O3 contributions reached up to 1.78 μg/m3 and 1.52 μg/m3 for cement and power plants, respectively. In terms of continuous emissions, cement plants exert the strongest influence within 0-2 km through rapid mixing and stronger local photochemical formation, while both cement and power plants make high O3 contributions again within a range of 5-13 km via regional transport and sustained chemical processes, forming exposure hotspots of regulatory concern. This spatial differentiation reveals overlooked far-field persistence beyond conventional near-field assessments. Wind-resolved analysis indicated that continuous industrial NOx emissions can exert stronger effects in downwind regions than near the source, highlighting their extended influence range.