Environmental Research Letters (Jan 2021)
Spatial and temporal distribution characteristics of ground-level nitrogen dioxide and ozone across China during 2015–2020
Abstract
In recent years, the emissions control in nitrogen oxides (NO _x ) was conducted across China, but how the concentrations of NO _x and its product ozone (O _3 ) in the atmosphere varied in space and time remains uncertain. Here, the spatial and temporal distributions of nitrogen dioxide (NO _2 ) and O _3 in 348 cities of China based on the hourly concentrations data during 2015–2020 were investigated, and the relationships among NO _2 , O _3 and meteorological and socioeconomic parameters were explored. It is shown that higher NO _2 and O _3 concentrations were mainly distributed in North, East and Central China, which are economically developed and densely populated regions. The annual mean concentrations of NO _2 increased from 2015 to 2017 but decreased from 2017 to 2020. The annual variations in O _3 generally exhibited an upward trend in 2015–2019 but decreased by 5% from 2019 to 2020. About 74% and 78% of cities had a decline in NO _2 and O _3 in 2020, respectively, compared to 2019, due to the limits of the motorized transports and industrial production activities during COVID-19 lockdown. The monthly mean concentrations of NO _2 showed an unusual decrease in February in all regions due to the reduced emissions during the Chinese Spring Festival holidays. Compared to 2019, the mean concentrations of NO _2 in January, February and March, 2020 during COVID-19 lockdown decreased by 16%, 28% and 20%, respectively; O _3 increased by 13% and 14% in January and February, respectively, but decreased by 2% in March, 2020. NO _2 and O _3 concentrations are likely associated with anthropogenic and natural emissions. In addition, meteorological parameters can affect NO _2 and O _3 concentrations by influencing the production process, the diffusion and local accumulation, and the regional circulations.
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