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. 2022 Jul 19;67(17):1745–1749. doi: 10.1016/j.scib.2022.07.021

Fig. 1.

Fig. 1

Ambient NH3 concentrations at 36 sites during the pre-COVID (1–26 January 2020) and COVID-lockdown (27 January–26 February 2020) periods (a), and average concentrations for rural, urban, and background sites (b). Daily mean NH3 concentrations at urban site in Beijing and urban and rural sites in Shanghai city (c), and average concentrations during the pre-COVID and COVID-lockdown period (d). Daily mean ε(NH4+) at urban site in Beijing and urban and rural sites in Shanghai city (e), and average concentrations during the pre-COVID and COVID-lockdown period (f). The letters R, U, and B denote, respectively, rural, urban and background sites.