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Impacts of the COVID-19 lockdown on atmospheric oxidizing capacity and secondary aerosol formation over the Beijing-Tianjin-Hebei region in Winter-Spring 2020
https://orcid.org/0000-0002-5623-1225
https://orcid.org/0000-0003-3733-0313
https://orcid.org/0000-0003-2354-0221
Abstract By using WRF-Chem coupled with a heterogeneous reaction mechanism for sulfate formation, this study investigated the impact of meteorological condition and emission changes on chemical species, atmospheric oxidizing capacity (AOC), and secondary aerosol formation during the COVID-19 lockdown period from 23 January to April 8, 2020, focusing on a severe haze event on 7–14 February. The model with the new sulfate formation scheme reasonably reproduces the spatial-temporal distribution of meteorological variables and chemical species, and significantly improves predictions for both sulfate and SO2 concentrations, as well as for PM2.5, ammonium, and nitrate to some extent. It is found that the adverse meteorological conditions were the main cause for the haze event formation, whereas emission reduction due to the lockdown somewhat decreased PM2.5 concentration on average in the Beijing-Tianjin-Hebei (BTH) region. Compared with the same period in 2019, increased surface air temperature and relative humidity (RH) and decreased planetary boundary layer height (PBLH) facilitated accumulation of pollutants and formation of secondary aerosols during the haze episode in 2020, whereas the emission reduction due to the lockdown led to decreases in SO2, NO2, primary PM2.5 (PPM2.5), black carbon (BC), primary organic aerosols (POA), nitrate and ammonium concentrations, but increases in O3, sulfate and secondary organic aerosol (SOA) concentrations, due to the combined effect of changes in emissions and AOC. Gas and aqueous phase oxidation of SO2 accounted for approximately 24% of sulfate formation, while the heterogeneous reaction of Mn-catalytic oxidation of SO2 on aerosol surfaces dominated sulfate formation (76%) during the haze episode in the BTH region. Both adverse meteorological conditions and emission reductions increased heterogeneous sulfate formation rate mainly through altering aerosol surface area (ASA), pH, and Mn2+ concentration. Chemical species varied diversely during the three subperiods before (Period-1, 15–22 January) and during the lockdown (Period-2, 23 January to 5 March and Period-3, 6 March to 8 April) over the BTH. NO2 concentration firstly decreased and then rebounded, whereas O3 concentration increased gradually from the Period-1 to Period-3. All aerosols except SOA decreased throughout the lockdown period, whereas SOA peaked in the Period-2 due to its strong sensitivity to increasing AOC. Sulfate concentration decreased from the Period-1 to Period-2, mainly due to more adverse meteorological conditions in the Period-1, although sulfate increased slightly due to increasing AOC in the Period-2. The large difference in the direction and magnitude of species variations during the COVID-19 lockdown indicates the complex interplay among meteorology, emission, and chemistry.
Graphical abstract The model simulated mean differences in near surface species concentrations between the BASE and EMIS19 cases (BASE minus EMIS19) during the haze period of 7–14 February 2020, representing the impact of emission reduction due to the COVID-19 lockdown on the chemical species. The units for PM2.5 and aerosol components are μg·m−3, and the units for SO2, NO2, and O3 are ppb. Display Omitted
Highlights Heterogeneous sulfate formation by Mn-catalytic reaction was coupled into WRF-Chem. Haze event during the COVID lockdown was caused by adverse meteorological conditions. Emission reduction led to a decrease in PM2.5 in Beijing but increases in portions of the BTH. Sulfate and SOA increased but nitrate decreased in the BTH in response to the lockdown.
Impacts of the COVID-19 lockdown on atmospheric oxidizing capacity and secondary aerosol formation over the Beijing-Tianjin-Hebei region in Winter-Spring 2020
https://orcid.org/0000-0002-5623-1225
https://orcid.org/0000-0003-3733-0313
https://orcid.org/0000-0003-2354-0221
Abstract By using WRF-Chem coupled with a heterogeneous reaction mechanism for sulfate formation, this study investigated the impact of meteorological condition and emission changes on chemical species, atmospheric oxidizing capacity (AOC), and secondary aerosol formation during the COVID-19 lockdown period from 23 January to April 8, 2020, focusing on a severe haze event on 7–14 February. The model with the new sulfate formation scheme reasonably reproduces the spatial-temporal distribution of meteorological variables and chemical species, and significantly improves predictions for both sulfate and SO2 concentrations, as well as for PM2.5, ammonium, and nitrate to some extent. It is found that the adverse meteorological conditions were the main cause for the haze event formation, whereas emission reduction due to the lockdown somewhat decreased PM2.5 concentration on average in the Beijing-Tianjin-Hebei (BTH) region. Compared with the same period in 2019, increased surface air temperature and relative humidity (RH) and decreased planetary boundary layer height (PBLH) facilitated accumulation of pollutants and formation of secondary aerosols during the haze episode in 2020, whereas the emission reduction due to the lockdown led to decreases in SO2, NO2, primary PM2.5 (PPM2.5), black carbon (BC), primary organic aerosols (POA), nitrate and ammonium concentrations, but increases in O3, sulfate and secondary organic aerosol (SOA) concentrations, due to the combined effect of changes in emissions and AOC. Gas and aqueous phase oxidation of SO2 accounted for approximately 24% of sulfate formation, while the heterogeneous reaction of Mn-catalytic oxidation of SO2 on aerosol surfaces dominated sulfate formation (76%) during the haze episode in the BTH region. Both adverse meteorological conditions and emission reductions increased heterogeneous sulfate formation rate mainly through altering aerosol surface area (ASA), pH, and Mn2+ concentration. Chemical species varied diversely during the three subperiods before (Period-1, 15–22 January) and during the lockdown (Period-2, 23 January to 5 March and Period-3, 6 March to 8 April) over the BTH. NO2 concentration firstly decreased and then rebounded, whereas O3 concentration increased gradually from the Period-1 to Period-3. All aerosols except SOA decreased throughout the lockdown period, whereas SOA peaked in the Period-2 due to its strong sensitivity to increasing AOC. Sulfate concentration decreased from the Period-1 to Period-2, mainly due to more adverse meteorological conditions in the Period-1, although sulfate increased slightly due to increasing AOC in the Period-2. The large difference in the direction and magnitude of species variations during the COVID-19 lockdown indicates the complex interplay among meteorology, emission, and chemistry.
Graphical abstract The model simulated mean differences in near surface species concentrations between the BASE and EMIS19 cases (BASE minus EMIS19) during the haze period of 7–14 February 2020, representing the impact of emission reduction due to the COVID-19 lockdown on the chemical species. The units for PM2.5 and aerosol components are μg·m−3, and the units for SO2, NO2, and O3 are ppb. Display Omitted
Highlights Heterogeneous sulfate formation by Mn-catalytic reaction was coupled into WRF-Chem. Haze event during the COVID lockdown was caused by adverse meteorological conditions. Emission reduction led to a decrease in PM2.5 in Beijing but increases in portions of the BTH. Sulfate and SOA increased but nitrate decreased in the BTH in response to the lockdown.
Impacts of the COVID-19 lockdown on atmospheric oxidizing capacity and secondary aerosol formation over the Beijing-Tianjin-Hebei region in Winter-Spring 2020
https://orcid.org/0000-0002-5623-1225
https://orcid.org/0000-0003-3733-0313
https://orcid.org/0000-0003-2354-0221
Abstract By using WRF-Chem coupled with a heterogeneous reaction mechanism for sulfate formation, this study investigated the impact of meteorological condition and emission changes on chemical species, atmospheric oxidizing capacity (AOC), and secondary aerosol formation during the COVID-19 lockdown period from 23 January to April 8, 2020, focusing on a severe haze event on 7–14 February. The model with the new sulfate formation scheme reasonably reproduces the spatial-temporal distribution of meteorological variables and chemical species, and significantly improves predictions for both sulfate and SO2 concentrations, as well as for PM2.5, ammonium, and nitrate to some extent. It is found that the adverse meteorological conditions were the main cause for the haze event formation, whereas emission reduction due to the lockdown somewhat decreased PM2.5 concentration on average in the Beijing-Tianjin-Hebei (BTH) region. Compared with the same period in 2019, increased surface air temperature and relative humidity (RH) and decreased planetary boundary layer height (PBLH) facilitated accumulation of pollutants and formation of secondary aerosols during the haze episode in 2020, whereas the emission reduction due to the lockdown led to decreases in SO2, NO2, primary PM2.5 (PPM2.5), black carbon (BC), primary organic aerosols (POA), nitrate and ammonium concentrations, but increases in O3, sulfate and secondary organic aerosol (SOA) concentrations, due to the combined effect of changes in emissions and AOC. Gas and aqueous phase oxidation of SO2 accounted for approximately 24% of sulfate formation, while the heterogeneous reaction of Mn-catalytic oxidation of SO2 on aerosol surfaces dominated sulfate formation (76%) during the haze episode in the BTH region. Both adverse meteorological conditions and emission reductions increased heterogeneous sulfate formation rate mainly through altering aerosol surface area (ASA), pH, and Mn2+ concentration. Chemical species varied diversely during the three subperiods before (Period-1, 15–22 January) and during the lockdown (Period-2, 23 January to 5 March and Period-3, 6 March to 8 April) over the BTH. NO2 concentration firstly decreased and then rebounded, whereas O3 concentration increased gradually from the Period-1 to Period-3. All aerosols except SOA decreased throughout the lockdown period, whereas SOA peaked in the Period-2 due to its strong sensitivity to increasing AOC. Sulfate concentration decreased from the Period-1 to Period-2, mainly due to more adverse meteorological conditions in the Period-1, although sulfate increased slightly due to increasing AOC in the Period-2. The large difference in the direction and magnitude of species variations during the COVID-19 lockdown indicates the complex interplay among meteorology, emission, and chemistry.
Graphical abstract The model simulated mean differences in near surface species concentrations between the BASE and EMIS19 cases (BASE minus EMIS19) during the haze period of 7–14 February 2020, representing the impact of emission reduction due to the COVID-19 lockdown on the chemical species. The units for PM2.5 and aerosol components are μg·m−3, and the units for SO2, NO2, and O3 are ppb. Display Omitted
Highlights Heterogeneous sulfate formation by Mn-catalytic reaction was coupled into WRF-Chem. Haze event during the COVID lockdown was caused by adverse meteorological conditions. Emission reduction led to a decrease in PM2.5 in Beijing but increases in portions of the BTH. Sulfate and SOA increased but nitrate decreased in the BTH in response to the lockdown.
Impacts of the COVID-19 lockdown on atmospheric oxidizing capacity and secondary aerosol formation over the Beijing-Tianjin-Hebei region in Winter-Spring 2020
Li, Yue (author) / Han, Zhiwei (author) / Song, Yu (author) / Li, Jiawei (author) / Sun, Yele (author) / Wang, Tiantian (author)
Atmospheric Environment ; 295
2022-12-11
Article (Journal)
Electronic Resource
English
Secondary aerosol formation in winter haze over the Beijing-Tianjin-Hebei Region, China
| Springer Verlag | 2021