Deseasonalized trend of ground-level ozone and its precursors in an industrial city Kaohsiung, Taiwan

• Published in: Environmental pollution (1987) 2024-06, Vol.351, p.124036, Article 124036
• Main Authors: Nguyen, Duy-Hieu, Liao, Chih-Hsiang, Bui, Xuan-Thanh, Wang, Lin-Chi, Yuan, Chung-Shin, Lin, Chitsan
• Format: Article
• Language: English
• Subjects: air; autumn; Autumn ozone month; data collection; industrialization; Long-term trend analysis; mountains; nitrogen; Nocturnal ozone; NOx titration; ozone; Ozone spatial variation; pollution; seasonal variation; Taiwan; titration; Total oxidant; wind; winter
• ISSN: 0269-7491; 1873-6424; 1873-6424
• DOI: 10.1016/j.envpol.2024.124036

Mitigating ground-level ozone (GLO) remains challenging due to its highly nonlinear formation process. Thus, understanding GLO pollution trends is crucial for developing effective control strategies, especially Kaohsiung industrial city, Taiwan. Based on the long-term monitoring data set of 2011–2022, temporal analysis reveals that monthly mean GLO peaks in autumn (40.66 ± 5.10 ppb), carbon monoxide (CO) and major precursors such as nitrogen oxides (NOx), nonmethane hydrocarbons (NMHC) reach their highest levels in winter. The distinct seasonal variation of air pollutants in Kaohsiung is primarily influenced by the unique blocking effect of the mountainous area under the northeasterly wind, as the city is situated downwind, causing high GLO levels during autumn due to the accumulation of stagnant air hindering the dispersion of pollutants. Over the 12 years (2011–2022), the deseasonalized trend analysis was conducted with p 120 ppb) decrease, days within midrange (60–80 ppb) rise from 24.4% to 33.3%. A notable difference emerges when comparing daytime and nighttime GLO. While daytime GLO decreased at −0.22 ppb/yr, nighttime GLO increased at +0.34 ppb/yr. Weakened nocturnal titration effects accounted for the nighttime increase. The distinct spatial variations in GLO trends on a citywide scale underscore that areas with complicated industrial activities may not benefit from a continuing reduction of precursors compared to less-polluted areas. The findings of this study hold significant implications for improving GLO control strategies in heavily industrialized city and provide valuable information to the general public about the current state of GLO pollution. [Display omitted] •Deseasonalized trends of major pollutants over Kaohsiung (2011–2022) are reported.•Autumn has the highest ground-level ozone levels, followed by spring, winter and summer.•Deseasonalized ground-level ozone trend remained stable under a drastic decrease of total oxidants.•Air quality improvement was supported by high ozone (>120 ppb) reduced while midrange ozone (60–80 ppb) raised.•Notable opposing trends between da