Quantitative assessment of surface particulate matter concentrations change over China during the COVID-19 pandemic and its implication to Chinese economic activities

Abstract:

Sixty days after the lockdown of Hubei province where the coronavirus was first reported, China seems to be recovering from the pandemic, but its true recovery remains an outstanding question. In this study, we investigate how human activity has changed during this period using surface pollutant observations. By combining surface data with a three-dimensional chemistry model, the impact of meteorological variations and yearly emissions control variations are minimized to demonstrate how the pollutant level over China changed before and after Lunar New Year during 2017–2020. The results show that the reduction in NO₂ concentrations, an indicator of emissions in the transportation sector, was clearly deeper and longer in 2020 than in normal years, and started to recover after February 15. On the contrary, the level of PM_2.5 emissions had not yet recovered by the end of March with a ~30% reduction compared with normal years. Additional model study using a top-down emission adjustment also confirms that a reduction of ~25% of unknown surface PM_2.5 emissions still exists during the same period even after SO₂ and NOx emissions are realistically updated. This evidence suggests that China may be experiencing different economic recovery speeds for different sectors, with the fastest recovery in the transportation sector and a slower recovery likely in the agricultural sector.