| Title: | Taiwan ozone trend in response to reduced domestic precursors and perennial transboundary influence |
| Author(s): | Chen SP; Liu WT; Hsieh HC; Wang JL; |
| Address: | "Department of Chemistry, National Central University, Taoyuan, Taiwan. Center for Environmental Monitoring and Technology, National Central University, Taoyuan, Taiwan. Department of Chemistry, National Central University, Taoyuan, Taiwan. Electronic address: cwang@cc.ncu.edu.tw" |
| DOI: | 10.1016/j.envpol.2021.117883 |
| ISSN/ISBN: | 1873-6424 (Electronic) 0269-7491 (Linking) |
| Abstract: | "Two decades of nitrogen oxides (NO(x)) and volatile organic compounds (VOCs) in ambient concentrations have been continuously reduced by nearly 60% since 1994. However, the annual mean ozone (O(3)) concentrations in Taiwan had leveled off for more than a decade. Furthermore, the significant cuts in precursors did lead to reduction in episodic days (O(3)>/= 100 ppbv) over time, implying the weakened photochemical production of O(3). Simultaneously, the number of low O(3) days (O(3) < 20 ppbv) also decreased due to weakened NO titration. Nevertheless, the reduction of both high and low O(3) days resulted in an increase in the number of medium O(3) days (O(3) from 60-80 ppbv). While the nighttime mean O(3) continued to increase, the daytime mean O(3) leveled off and coincided with the marine background concentration of approximately 40 ppbv, revealing a gradual decrease in the daytime-nighttime mean O(3) difference. In addition to multiple chemical reasons, transboundary O(3) from Asian continental outflow is thought to be another major contributor to the prolonged leveling of domestic O(3). To quantitatively illustrate the role of the transboundary effect, model simulations were conducted in two ways: one assessed the time percentage of a year affected by the transboundary influence; and the other involved decoupling the transboundary O(3) from the domestically produced O(3) to quantify the amount of domestic O(3) that can be mitigated by prescribing scenarios; namely, the so-called sensitivity test. The sensitivity test suggests that although controlling domestic emissions is still vital to contain O(3) under weak transboundary conditions, the overall O(3) averages and the long-term trend at the island scale are closely associated with the transboundary influence. The gradual increased medium O(3) concentrations to approximate the marine background level could imply that future O(3) concentration on the island will be more influenced more by the transboundary conditions and less relevant to the domestic containment measures" |
| Keywords: | *Air Pollutants/analysis Environmental Monitoring *Ozone/analysis Taiwan *Volatile Organic Compounds/analysis Asian continental outflow Long-term trend analysis Model simulation Ozone; |
| Notes: | "MedlineChen, Sheng-Po Liu, Wen-Tzu Hsieh, Hsin-Cheng Wang, Jia-Lin eng England 2021/08/25 Environ Pollut. 2021 Nov 15; 289:117883. doi: 10.1016/j.envpol.2021.117883. Epub 2021 Jul 31" |
