Drastic Changes of PM_2.5 Trans-Boundary Pollution over Japan Due to COVID-19 Lockdown in China

Abstract

In order to prevent the spread of COVID-19, the Chinese government imposed a lockdown. During this period, anthropogenic emissions will be reduced; therefore, the trans-boundary air pollution will be changed. The analysis of surface observations by the automated aerosol chemical speciation analyzer (ACSA) showed that the dramatic reduction with 30–50% of PM_2.5, sulfate (SO₄²⁻), and nitrate (NO₃⁻) on February–March 2020 compared to 2018–2019. The results of the chemical transport model suggested that the reduction of SO₄²⁻ was mostly caused by SO₂ emission reduction whereas that of NO₃⁻ was dominated by the meteorological variability. The record high warm winter on 2020 was related to the unfavorable condition to produce NO₃⁻.