Journal Article

Insights on ozone formation sensitivity in Southeast and East Asian megacities during ASIA-AQ

Lesko, Kirk, Lee, Young Ro, Ball, Katherine, Jeong, Daun, Tanner, David J., Miech, Jason, Crawford, James, Wojnowski, Wojciech, Diskin, Glenn S., Sebol, Abby, St. Clair, Jason M., Hall, Samuel R., Ullmann, Kirk, Hannun, Reem A., Roozitalab, Behrooz, Wennberg, Paul O., Wisthaler, Armin, Apel, Eric C., Hills, Alan J., Choi, Yonghoon, DiGangi, Joshua P., Liao, Jin, Delaria, Erin R., Meinardi, Simone, Barletta, Barbara, Min, Kyung-Eun, Kang, Heejoo, Piel, Felix, Wolfe, Glenn M., Flocke, Frank, Hanisco, Thomas F., Arterburn, Linda, Blake, Donald R., Blake, Nicola J., Franchin, Alessandro, Cho, Changmin, Hornbrook, Rebecca S., Nam, Woohui, Owen, Courtney, Dibb, Jack, Huey, L. Gregory

2026

Overview

Controlling ozone (O3) in rapidly urbanizing megacities in Southeast and East Asia remains a challenge. O3 is a secondary pollutant formed through nonlinear photochemical reactions with its precursors: nitrogen oxides (NOx) and volatile organic compounds (VOCs). Observation-based quantification of precursor sensitivity remains scarce, limiting actionable O3 control. To address this, we leverage airborne observations from the NASA DC-8 during the ASIA-AQ campaign conducted in February and March 2024 across four Asian megacities: Metro Manila, the Seoul Metropolitan Area, the Tainan–Kaohsiung Metropolitan Area, and the Bangkok Metropolitan Region. These extensive measurements of various trace gases were used to constrain a zero-dimensional box model and estimate the net production rates of Ox (POx, Ox = O3 + NO2). Precursor sensitivity regimes were characterized for each megacity by generating isopleths of POx across varying levels of NOx and VOCs. The analysis revealed that Manila and Tainan–Kaohsiung exhibited predominantly NOx-sensitive conditions, favoring NOx reduction as an effective O3 mitigation strategy, while Bangkok showed a more mixed sensitivity, suggesting combined NOx and VOC reductions. In contrast, Seoul exhibited a primarily VOC-sensitive regime associated with its higher NOx conditions relative to the other cities, underscoring the importance of VOC-focused strategies. In addition, to quantitatively assess sensitivity transitions, we computed orthogonal distances from the isopleth transition boundaries for all four study areas. Diurnal analyses of these distances revealed a shift from more VOC-sensitive conditions in the morning toward more NOx-sensitive regimes in the afternoon. These findings provide critical insights for formulating effective, city-specific O3 control policies in urban environments.

• Publisher: Copernicus GmbH,Copernicus Publications
• Subject: Agricultural production / Air pollution / Aircraft / Analysis / Chemicals / Cities / Emissions / Isopleths / Megacities / Metropolitan areas / Nitrogen compounds / Nitrogen dioxide / Nitrogen oxide / Nitrogen oxides / Nomograms / Outdoor air quality / Ozone / Ozone formation / Photochemical reactions / Photochemicals / Photochemistry / Pollutants / Precursors / Ratios / Satellites / Sensitivity analysis / Trace gases / Urban environments / VOCs / Volatile organic compounds