The impact of COVID-19 lockdowns on urban photochemistry as inferred from TROPOMI

Srijana Lama; Sander Houweling; K. Folkert Boersma; Ilse Aben; Hugo A.C.Denier van der Gon; Maarten C. Krol

doi:10.1016/j.atmosenv.2023.120042

The impact of COVID-19 lockdowns on urban photochemistry as inferred from TROPOMI

Srijana Lama^*, Sander Houweling, K. Folkert Boersma, Ilse Aben, Hugo A.C.Denier van der Gon, Maarten C. Krol

^*Corresponding author for this work

Earth Sciences

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Movement restrictions were imposed in 2020 to mitigate the spread of Covid-19. These lock-down episodes provide a unique opportunity to study the sensitivity of urban photochemistry to temporary emission reductions and test air quality models. This study uses Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide/carbon monoxide (NO₂/CO) ratios in urban plumes in combination with an exponential fitting procedure to infer changes in the NOx lifetime (τ_NOx) during Covid-19 lock-downs in the cities of Denver, Chicago, New York, Riyadh, Wuhan and Sao Paulo compared with the year before. The strict lockdown policy in Wuhan led to a 65–80% reduction in NO₂, compared to 30–50% in the other cities that were studied. In New York and Wuhan, CO concentration was reduced by 10–15%, whereas over Riyadh, Denver, Chicago, and Sao Paulo the CO background concentration increased by 2–5 ppb. τ_NOx has been derived for calm (0.0 < U (m/s) < 3.5) and windy (5.0 < U (m/s) < 8.5) days to study the influence of wind speed. We find reductions in τ_NOx during Covid-19 lockdowns in all six megacities during calm days. The largest change in τ_NOx during calm days is found for Sao-Paulo (31.8 ± 9.0%), whereas the smallest reduction is observed over Riyadh (22 ± 6.6%). During windy days, reductions in τ_NOx are observed during Covid-19 lockdowns in New York and Chicago. However, over Riyadh τ_NOx is almost similar for windy days during the Covid-19 lockdown and the year before. Ground-based measurements and the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model have been used to validate the TROPOMI-derived results over Denver. CLASS simulates an enhancement of ozone (O₃) by 4 ppb along with reductions in NO (38.7%), NO₂ (25.7%) and CO (17.2%) during the Covid-19 lockdown in agreement with the ground-based measurements. In CLASS, decreased NO_x emissions reduce the removal of OH in the NO₂ + OH reaction, leading to higher OH concentrations and decreased τ_NOx. The reduction in τ_NOx inferred from TROPOMI (28 ± 9.0%) is in agreement with CLASS. These results indicate that TROPOMI derived NO₂/CO ratios provide useful information about urban photochemistry and that changes in photochemical lifetimes can successfully be detected.

Original language	English
Article number	120042
Pages (from-to)	1-12
Number of pages	12
Journal	Atmospheric Environment
Volume	312
Early online date	18 Aug 2023
DOIs	https://doi.org/10.1016/j.atmosenv.2023.120042
Publication status	Published - 1 Nov 2023

Bibliographical note

Funding Information:
In this study, the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model (van Stratum et al., 2012) has been used to support the interpretation of TROPOMI-estimated changes in the urban photochemistry due to the Covid-19 lockdown in Denver. In CLASS the daytime boundary layer growth is determined mostly by the sensible and latent heat fluxes and the entrainment of air from free troposphere. CLASS is a box model for well mixed atmospheric conditions, capable of successfully reproducing the observed mixing ratios of air pollutants and meteorological variables in the turbulent boundary layer (Van Stratum et al., 2012).This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model.

Funding Information:
This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036 ). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model.

Publisher Copyright:
© 2023 The Authors

Funding

In this study, the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model (van Stratum et al., 2012) has been used to support the interpretation of TROPOMI-estimated changes in the urban photochemistry due to the Covid-19 lockdown in Denver. In CLASS the daytime boundary layer growth is determined mostly by the sensible and latent heat fluxes and the entrainment of air from free troposphere. CLASS is a box model for well mixed atmospheric conditions, capable of successfully reproducing the observed mixing ratios of air pollutants and meteorological variables in the turbulent boundary layer (Van Stratum et al., 2012).This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model. This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036 ). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model.

Keywords

Cities
CO
Covid-19
NO
NOx lifetime
TROPOMI

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title = "The impact of COVID-19 lockdowns on urban photochemistry as inferred from TROPOMI",

abstract = "Movement restrictions were imposed in 2020 to mitigate the spread of Covid-19. These lock-down episodes provide a unique opportunity to study the sensitivity of urban photochemistry to temporary emission reductions and test air quality models. This study uses Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide/carbon monoxide (NO2/CO) ratios in urban plumes in combination with an exponential fitting procedure to infer changes in the NOx lifetime (τNOx) during Covid-19 lock-downs in the cities of Denver, Chicago, New York, Riyadh, Wuhan and Sao Paulo compared with the year before. The strict lockdown policy in Wuhan led to a 65–80% reduction in NO2, compared to 30–50% in the other cities that were studied. In New York and Wuhan, CO concentration was reduced by 10–15%, whereas over Riyadh, Denver, Chicago, and Sao Paulo the CO background concentration increased by 2–5 ppb. τNOx has been derived for calm (0.0 < U (m/s) < 3.5) and windy (5.0 < U (m/s) < 8.5) days to study the influence of wind speed. We find reductions in τNOx during Covid-19 lockdowns in all six megacities during calm days. The largest change in τNOx during calm days is found for Sao-Paulo (31.8 ± 9.0%), whereas the smallest reduction is observed over Riyadh (22 ± 6.6%). During windy days, reductions in τNOx are observed during Covid-19 lockdowns in New York and Chicago. However, over Riyadh τNOx is almost similar for windy days during the Covid-19 lockdown and the year before. Ground-based measurements and the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model have been used to validate the TROPOMI-derived results over Denver. CLASS simulates an enhancement of ozone (O3) by 4 ppb along with reductions in NO (38.7%), NO2 (25.7%) and CO (17.2%) during the Covid-19 lockdown in agreement with the ground-based measurements. In CLASS, decreased NOx emissions reduce the removal of OH in the NO2 + OH reaction, leading to higher OH concentrations and decreased τNOx. The reduction in τNOx inferred from TROPOMI (28 ± 9.0%) is in agreement with CLASS. These results indicate that TROPOMI derived NO2/CO ratios provide useful information about urban photochemistry and that changes in photochemical lifetimes can successfully be detected.",

keywords = "Cities, CO, Covid-19, NO, NOx lifetime, TROPOMI",

author = "Srijana Lama and Sander Houweling and Boersma, {K. Folkert} and Ilse Aben and {van der Gon}, {Hugo A.C.Denier} and Krol, {Maarten C.}",

note = "Funding Information: In this study, the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model (van Stratum et al., 2012) has been used to support the interpretation of TROPOMI-estimated changes in the urban photochemistry due to the Covid-19 lockdown in Denver. In CLASS the daytime boundary layer growth is determined mostly by the sensible and latent heat fluxes and the entrainment of air from free troposphere. CLASS is a box model for well mixed atmospheric conditions, capable of successfully reproducing the observed mixing ratios of air pollutants and meteorological variables in the turbulent boundary layer (Van Stratum et al., 2012).This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model. Funding Information: This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036 ). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model. Publisher Copyright: {\textcopyright} 2023 The Authors",

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doi = "10.1016/j.atmosenv.2023.120042",

language = "English",

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AU - Lama, Srijana

AU - Houweling, Sander

AU - Boersma, K. Folkert

AU - Aben, Ilse

AU - van der Gon, Hugo A.C.Denier

AU - Krol, Maarten C.

N1 - Funding Information: In this study, the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model (van Stratum et al., 2012) has been used to support the interpretation of TROPOMI-estimated changes in the urban photochemistry due to the Covid-19 lockdown in Denver. In CLASS the daytime boundary layer growth is determined mostly by the sensible and latent heat fluxes and the entrainment of air from free troposphere. CLASS is a box model for well mixed atmospheric conditions, capable of successfully reproducing the observed mixing ratios of air pollutants and meteorological variables in the turbulent boundary layer (Van Stratum et al., 2012).This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model. Funding Information: This research has been supported by the Aard- en Levenswetenschappen, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (grant no. 2017.036 ). Thanks to prof Dr. Jordi Vila-Guerau de Arellano for providing the guidance to setup CLASS model. Publisher Copyright: © 2023 The Authors

PY - 2023/11/1

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N2 - Movement restrictions were imposed in 2020 to mitigate the spread of Covid-19. These lock-down episodes provide a unique opportunity to study the sensitivity of urban photochemistry to temporary emission reductions and test air quality models. This study uses Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide/carbon monoxide (NO2/CO) ratios in urban plumes in combination with an exponential fitting procedure to infer changes in the NOx lifetime (τNOx) during Covid-19 lock-downs in the cities of Denver, Chicago, New York, Riyadh, Wuhan and Sao Paulo compared with the year before. The strict lockdown policy in Wuhan led to a 65–80% reduction in NO2, compared to 30–50% in the other cities that were studied. In New York and Wuhan, CO concentration was reduced by 10–15%, whereas over Riyadh, Denver, Chicago, and Sao Paulo the CO background concentration increased by 2–5 ppb. τNOx has been derived for calm (0.0 < U (m/s) < 3.5) and windy (5.0 < U (m/s) < 8.5) days to study the influence of wind speed. We find reductions in τNOx during Covid-19 lockdowns in all six megacities during calm days. The largest change in τNOx during calm days is found for Sao-Paulo (31.8 ± 9.0%), whereas the smallest reduction is observed over Riyadh (22 ± 6.6%). During windy days, reductions in τNOx are observed during Covid-19 lockdowns in New York and Chicago. However, over Riyadh τNOx is almost similar for windy days during the Covid-19 lockdown and the year before. Ground-based measurements and the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model have been used to validate the TROPOMI-derived results over Denver. CLASS simulates an enhancement of ozone (O3) by 4 ppb along with reductions in NO (38.7%), NO2 (25.7%) and CO (17.2%) during the Covid-19 lockdown in agreement with the ground-based measurements. In CLASS, decreased NOx emissions reduce the removal of OH in the NO2 + OH reaction, leading to higher OH concentrations and decreased τNOx. The reduction in τNOx inferred from TROPOMI (28 ± 9.0%) is in agreement with CLASS. These results indicate that TROPOMI derived NO2/CO ratios provide useful information about urban photochemistry and that changes in photochemical lifetimes can successfully be detected.

AB - Movement restrictions were imposed in 2020 to mitigate the spread of Covid-19. These lock-down episodes provide a unique opportunity to study the sensitivity of urban photochemistry to temporary emission reductions and test air quality models. This study uses Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide/carbon monoxide (NO2/CO) ratios in urban plumes in combination with an exponential fitting procedure to infer changes in the NOx lifetime (τNOx) during Covid-19 lock-downs in the cities of Denver, Chicago, New York, Riyadh, Wuhan and Sao Paulo compared with the year before. The strict lockdown policy in Wuhan led to a 65–80% reduction in NO2, compared to 30–50% in the other cities that were studied. In New York and Wuhan, CO concentration was reduced by 10–15%, whereas over Riyadh, Denver, Chicago, and Sao Paulo the CO background concentration increased by 2–5 ppb. τNOx has been derived for calm (0.0 < U (m/s) < 3.5) and windy (5.0 < U (m/s) < 8.5) days to study the influence of wind speed. We find reductions in τNOx during Covid-19 lockdowns in all six megacities during calm days. The largest change in τNOx during calm days is found for Sao-Paulo (31.8 ± 9.0%), whereas the smallest reduction is observed over Riyadh (22 ± 6.6%). During windy days, reductions in τNOx are observed during Covid-19 lockdowns in New York and Chicago. However, over Riyadh τNOx is almost similar for windy days during the Covid-19 lockdown and the year before. Ground-based measurements and the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model have been used to validate the TROPOMI-derived results over Denver. CLASS simulates an enhancement of ozone (O3) by 4 ppb along with reductions in NO (38.7%), NO2 (25.7%) and CO (17.2%) during the Covid-19 lockdown in agreement with the ground-based measurements. In CLASS, decreased NOx emissions reduce the removal of OH in the NO2 + OH reaction, leading to higher OH concentrations and decreased τNOx. The reduction in τNOx inferred from TROPOMI (28 ± 9.0%) is in agreement with CLASS. These results indicate that TROPOMI derived NO2/CO ratios provide useful information about urban photochemistry and that changes in photochemical lifetimes can successfully be detected.

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The impact of COVID-19 lockdowns on urban photochemistry as inferred from TROPOMI

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