Ineffective implementation of emergency reduction measures against high concentrations of particulate matter in Seoul, Republic of Korea

Environ Monit Assess (2023) 195:1127 https://doi.org/10.1007/s10661-023-11754-0 RESEARCH Ineffective implementation of emergency reduction measures against high concentrations of particulate matter in Seoul, Republic of Korea Chang‑Hoi Ho · Ka‑Young Kim Received: 27 October 2022 / Accepted: 19 August 2023 © The Author(s) 2023 Abstract Since December 30, 2017, the Seoul Metropolitan Government, Republic of Korea, has been implementing emergency reduction measures (ERMs) restricting the operation of industrial sites, thermal power plants, and vehicles when air quality is expected to deteriorate. ERMs are implemented when the present observed concentration of particulate matter (PM) of aerodynamic diameter less than 2.5 μm (PM2.5) and/or the predicted values for the following day exceed a threshold value. In this study, the effectiveness of ERMs was evaluated for 33 days with and 6 days without ERM implementation but where the PM2.5 concentration exceeded the threshold value, until March 15, 2021. Of the 33 days of ERM implementation, on 7 days it was executed despite the thresholds not being met. The ERM on these days might have been properly executed because the pre-notice and implementation of ERM might have reduced the local emissions of air pollutants. Our major findings are that even on days of ERM implementation, there were marginal reductions in vehicle traffic, thermal power generation, and industrial emissions. Second, the concentrations of PM2.5 and related air pollutants in Seoul were almost unchanged for most ERM implementation episodes. Third, most C.-H. Ho (*) · K.-Y. Kim School of Earth and Environmental Sciences, Seoul National University, 1 Gwanak‑Ro, Gwanak‑Gu, Seoul 08826, Republic of Korea e-mail: of the 39 (= 33 + 6) days when the air quality worsened were caused by the transboundary transport of air pollutants from China. In conclusion, it was revealed that the currently executed ERM law is insufficient for effectively reducing PM2.5. To achieve the required reductions, it is necessary to undertake stricter policies in Seoul and its neighboring regions. Keywords Air pollution · Emergency reduction measures · Emission source · Korea · Pollutants · Seoul · Traffic volume · Transboundary transport Introduction The Seoul Metropolitan Government has been implementing emergency reduction measures (ERMs) in Seoul, Republic of Korea (hereafter referred to as Korea), on days when extremely high levels of particulate matter (PM) with an aerodynamic diameter less than 2.5 μm (PM2.5) are expected to continue for a certain period (KME, 2019). The ERM law was enacted on March 15, 2015; however, it was first enforced on December 30, 2017, after supplementing various associated materials and increasing the accuracy of PM predictions for the next 1 to 2 days. When the ERM law was implemented, strong regulations were imposed on vehicle operations and various sources of air polluting emissions. By reducing, as far as possible, locally generated emissions in the Seoul area, a rapid increase in the concentration of PM2.5 Vol.: (0123456789) 13 1127 Page 2 of 16 can be alleviated, even when air pollutants flow into Seoul from surrounding regions. Nevertheless, ERM should be executed in a timely manner, because it causes an enormous inconvenience for social and economic activities (Choi et al., 2019b; Yoon, 2019). When ERM was promptly initiated on January 13–18, 2018, it was estimated that PM2.5 precursor emissions decreased by 26–49% (Joo et al., 2018). Lee et al. (2019b) suggested that emission amounts could be diminished by ERM, resulting in a 30% decrease in P M2.5 concentrations. In many countries, multiple policies have been implemented to decrease short-term PM concentrations when air quality is expected to be extremely poor. In China, odd–even vehicle schemes and a shutdown of emission sources were enforced in the Beijing–Tianjin–Hebei (BTH) region; these actions reduced daily mean PM2.5 concentrations by 20–30% (Wang et al., 2017, 2018). In contrast, there are some cases of trivial reduction effects due to significant inflows of air pollutants from neighboring regions (Lee et al., 2013; Oh et al., 2020). Considering that the above-mentioned studies generally reached their conclusions based on case studies, there was a limited ability to generalize the effectiveness of the reduction measures. Moreover, numerical modeling results have been used to artificially adjust emissions without aggregating the observed reductions in traffic volumes and power generation (Ma et al., 2020; Tian et al., 2019). While a total 33 days of ERM were implemented in a timely manner from the time the law was implemented until March 15, 2021, the number of days of high P M2.5 concentration has not significantly decreased (Lee et al., 2019b). For this reason, it is necessary to investigate not only the reduction in local emissions in the Seoul metropolitan region but also other influences from domestic emissions, transboundary transport, and atmospheric circulation (Chang et al., 2021; Lee et al., 2011, 2021; Oh et al., 2015). Under stagnant synoptic environments, locally emitted pollutants might not diffuse to the surroundings (Park et al., 2019), and transboundary transport pollutants can combine with local emissions to react chemically (Kim et al., 2017b; Seo et al., 2017); thus, extremely high concentrations of PMs could last for several days. It should be noted that Korea is located on the windward side of China; thus, the air quality may deteriorate due to the inflow of transboundary air pollutants from China (e.g., Bae et al., 2019; Vol:. (1234567890) 13 Environ Monit Assess (2023) 195:1127 Chang et al., 2021; Kim et al., 2017b, 2016a; Lee et al., 2013). During the period of high P M2.5 concentrations in Seoul, the contribution from China was 60–80% (e.g., Choi et al., 2019a; Kim et al., 2018; Koo et al., 2008; Oh et al., 2020). ERM is a critical national issue; however, no research has quantitatively evaluated the effectiveness of the policy. In this study, the effect of ERM was examined by comparing the P M2.5 concentrations for four categories of ERM: proper (ERM-proper), late (ERM-delay), effective or improper (ERM-uncertain), and absent (ERM-miss) implementation. The “Materials and methods” section describes the data and methods used in this study. The “Results and discussion” section analyzes changes in PM2.5 concentration and air quality variables before and after the period of ERM for the four categories. The domestic and foreign contributions of P M2.5 in the Seoul area are also examined. The results are summarized in the “Conclusion” section. Materials and methods Air pollutant and meteorological data The daily mean concentrations of air pollutants— PM2.5, carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2)—were obtained from 25 air quality monitoring sites in Seoul during the cold seasons (November through March) of 2017–2021. The c (...truncated)