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

Duy-Hieu Nguyen; Chih-Hsiang Liao; Xuan-Thanh Bui; Lin-Chi Wang; Chung-Shin Yuan; Chitsan Lin

doi:10.1016/j.envpol.2024.124036

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

Environ Pollut. 2024 Apr 25:351:124036. doi: 10.1016/j.envpol.2024.124036. Online ahead of print.

Authors

Duy-Hieu Nguyen¹, Chih-Hsiang Liao², Xuan-Thanh Bui³, Lin-Chi Wang⁴, Chung-Shin Yuan⁵, Chitsan Lin⁶

Affiliations

¹ Program in Maritime Science and Technology, College of Maritime, National Kaohsiung University of Science and Technology, Kaohsiung, 811213, Taiwan.
² Department of Environmental Engineering and Science, Chia-Nan University of Pharmacy and Science, Tainan, 71710, Taiwan.
³ Key Laboratory of Advanced Waste Treatment Technology & Faculty of Environment and Natural Resources, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, 700000, Viet Nam; Vietnam National University Ho Chi Minh City (VNU-HCM), Linh Trung ward, Ho Chi Minh City, 700000, Viet Nam.
⁴ Department of Marine Environmental Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, 811213, Taiwan.
⁵ Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan.
⁶ Program in Maritime Science and Technology, College of Maritime, National Kaohsiung University of Science and Technology, Kaohsiung, 811213, Taiwan; Department of Marine Environmental Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, 811213, Taiwan. Electronic address: ctlin@nkust.edu.tw.

PMID: 38677459
DOI: 10.1016/j.envpol.2024.124036

Abstract

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 (NO_x), 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 < 0.001, revealing a stabilization trend of GLO (+0.04 ppb/yr) from a previous sharp increase. The observed improvement is credited to a drastic decrease in total oxidants (O_x) at -0.63 ppb/yr due to significantly reducing their precursors. Furthermore, the effectiveness of precursor reduction is also supported by GLO daily maximum profile changes. While high GLO events (>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.

Keywords: Autumn ozone month; Long-term trend analysis; NO(x) titration; Nocturnal ozone; Ozone spatial variation; Total oxidant.