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. 2022 Jul 18;13(8):101510. doi: 10.1016/j.apr.2022.101510

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Fig. 1 — Monthly average of PM_2.5 concentrations in China and Korea from January to March in 2019 and 2020. (a) Jing-Jin-Ji region (BTH). (b) Beijing. (c) Baengnyeong Island. (d) Seoul. The figure compares the average monthly concentration of PM_2.5 in 2020 compared to 2019. Error bars of Seoul and Baengnyeong Island indicate the standard deviations (SDs) of the observed hourly data. The error bars of the BTH indicate the SDs of PM_2.5 concentrations measured at monitoring stations in Beijing, Tianjin, and Hebei provinces. (e) Map of ground-based PM_2.5 monitoring regions. The dashed box indicates the BTH, Beijing, Baengnyeong Island, and Seoul.