Reductions in NO<sub>2</sub> concentrations in Seoul, South Korea detected from space and ground-based monitors prior to and during the COVID-19 pandemic

Seo, Seunghwan; Kim, Si‐Wan; Kim, Kyoung-Min; Lamsal, L. N.; Jin, Hyungah

doi:10.1088/2515-7620/abed92

Cited by 7 publications

(5 citation statements)

References 46 publications

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“…There is a decreasing trend over the 2015-2019 period as previously reported by Seo et al (2021), more so in summer than in winter.…”

Section: Airkorea Data and Trends 2015-2019supporting

confidence: 75%

“…Declining NO2 in the SMA can be attributed to policies to decrease vehicular NOx emissions (Kim and Lee, 2018). The weaker decline in winter is consistent with findings 160 from Seo et al (2021), who found that surface NO2 concentrations in the SMA in 2015-2019 declined by 5.3% a -1 during morning commute time for the ozone season, but only by 2.6% a -1 for the non-ozone season. The weaker response of NO2 to reduced NOx emissions in winter could be due to ozone titration by emitted NO, which would take place most systematically at night but also extend to daytime if the ozone supply is weak.…”

supporting

confidence: 79%

“…Using satellite and surface observations of NO2, Seo et al (2021) found that NOx emissions declined in Seoul by 30% during the 2015-2019 period, and Bae et al (2021) found a 18% decrease for the 2015-2018 period. On the other hand, Bauwens et al (2022) found an increase in satellite-observed HCHO columns over South Korea by 1-60 2% a -1 for the 2005-2019 period, which does not support a decrease in VOC emissions.…”

Section: Introduction 40mentioning

confidence: 99%

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Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Colombi

Jacob²,

Yang³

et al. 2022

Preprint

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Abstract. Surface ozone pollution in South Korea has increased over the past two decades, despite efforts to decrease emissions, and is pervasively in exceedance of the maximum daily 8-hr average (MDA8) standard of 60 ppb. Here, we investigate the 2015–2019 trends in surface ozone and NO2 concentrations over South Korea and the Seoul Metropolitan Area (SMA), focusing on the 90th percentile MDA8 ozone as an air quality metric. We use a random forest algorithm to remove the effect of meteorological variability on the 2015–2019 trends and find an emission-driven ozone increase of up to 1.5 ppb a-1 in April–May while NO2 decreases by 22 %. GEOS-Chem model simulations including recent chemical updates can successfully simulate surface ozone over South Korea and China as well as the very high free tropospheric ozone observed above 2 km altitude (mean 75 ppb in May–June), and can reproduce the observed 2015–2019 emission-driven ozone trend over the SMA including its seasonality. Further investigation of the model trend for May, when meteorology-corrected ozone and its increase are the highest, reveals that a decrease in South Korea NOx emissions is the main driver for the SMA ozone increase. Although this result implies that decreasing volatile organic compound (VOC) emissions is necessary to decrease ozone, we find that SMA ozone would still remain above 80 ppb even if all anthropogenic emissions in South Korea were shut off. China contributes only 8 ppb to this elevated South Korea background and ship emissions contribute only a few ppb. Zeroing out all anthropogenic emissions in East Asia in the model indicates a remarkably high external background of 56 ppb, consistent with the high concentrations observed in the free troposphere, implying that the air quality standard in South Korea is not practically achievable unless this background external to East Asia can be decreased.

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“…There is a decreasing trend over the 2015-2019 period as previously reported by Seo et al (2021), more so in summer than in winter.…”

Section: Airkorea Data and Trends 2015-2019supporting

confidence: 75%

supporting

confidence: 79%

Section: Introduction 40mentioning

confidence: 99%

See 1 more Smart Citation

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Colombi

Jacob²,

Yang³

et al. 2022

Preprint

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“…Gas‐phase precursors mainly emitted from fossil‐fuel combustion generate aqueous‐phase secondary aerosols with an aerodynamic diameter of less than 2.5 μm (PM 2.5 ) in the atmospheric boundary layer (Kumar et al., 2021; Wang, Ye, et al., 2021). Despite the decreased trend of anthropogenic precursors in eastern China since approximately 2006–2008 (Jia & Quaas, 2023; Lu et al., 2011), particularly during the COVID‐19 pandemic period from 2020, the occurrence of frequent severe hazes has persisted in eastern China and extended toward Korea (Cho et al., 2022; Seo et al., 2021; Shao et al., 2018; Wang, Wang, et al., 2021). This phenomenon is attributed to the heightened production of PM 2.5 through aqueous chemistry processes during transboundary transport (Cho et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

Influence of Aqueous‐Phase Chemistry on the Concentrations of PM_2.5 and Hydrometers During the Development of Convective Clouds Over the Yellow Sea in July of 2017

Cho,

Kim

2024

JGR Atmospheres

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Meteorological processes are investigated during the development of deep convective clouds over the Yellow Sea inside a quasi‐stationary rainy front in the East Asian region. WRF‐Chem simulations were conducted to assess the effects of aqueous‐phase chemistry on the concentrations of PM2.5 and hydrometers in deep convective clouds and the associated precipitation. A reduction in the south‐north air temperature gradient induced an inactive quasi‐stationary rainy front with nonlinear zonal clouds during the Changma period in the East Asian region in 2017, causing intensified surface heating due to solar radiation. A mesoscale cyclone was formed near the Shantung Peninsula inside the inactive quasi‐stationary rainy front, extending the eastward tongue of the troughs across the Yellow Sea. Deep convective clouds (CC16 on July 16, CC17 on July 17, and CC18 on July 18) formed in a severe mode on the east side of the mesoscale cyclone over the Yellow Sea at midnight as the warm type, as the warm and humid south‐southwesterly winds present at that time produced convection energy. PM2.5 from eastern China flowed into warm‐type CC16, CC17, and CC18 areas, producing more cloud droplets below 500 hPa via activation. In contrast, the release of additional condensation heat amplifies updrafts within convective clouds during efficient nighttime environmental cooling, thereby enhancing the production of cold‐type ice, reaching altitudes of up to 15 km. The WRF‐Chem PM2.5 outcomes indicate a significant increase in heavy rainfall, exceeding 10 mm hr−1, particularly in the context of the development of cold‐type convective clouds.

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“…Therefore, it would be useful to investigate ozone trends in South Korea separately for spring and summer. There were large changes in atmospheric composition during the COVID-19 pandemic (Bauwens et al, 2020;Koo et al, 2020;Seo et al, 2021). The deviations caused by the pandemic from the long-term trends would provide a valuable perspective for planning of future environmental policy to improve ozone pollution.…”

Section: Introductionmentioning

confidence: 99%

Changes in surface ozone in South Korea on diurnal to decadal time scale for the period of 2001–2021

Kim

Jeong

et al. 2022

Preprint

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Abstract. Increasing trends of tropospheric ozone in South Korea in the last decades have reported in several studies, based on various metrics. In this study, we derived the trends of surface ozone in South Korea utilizing the daily maximum 8-hours average ozone concentrations (MDA8) measured at the surface from 2001 to 2021 and analyzed diurnal, seasonal, multi-decadal variations of this parameter at city, province, and background sites. The 4th highest MDA8 values have positive trends at 7 cities and 8 provinces throughout 2001–2021 with approximately 1–2 ppb yr-1 and were greater than 70 ppb after early 2010 for all sites, despite decreases of its precursor NO2 and CO. The Seoul Metropolitan Area (SMA) and the background sites have different diurnal and seasonal characteristics of MDA8 exceedances defined in this study (percentage of the data points with MDA8 > 70 ppb among all data points). SMA have much higher exceedances during summer than spring, while the background sites have much higher exceedances during spring than summer highlighting efficient local production of ozone in SMA during summer and strong influence of long-range transport during spring. The exceedances during spring and summer are similar for the rest of sites. The peaks of exceedances occur at 4–5 PM in SMA and most of locations, while exceedances mainly occur at 7–8 PM through night at the background sites. During spring of the COVID-19 pandemic (2020–2021), the MDA8 ozone exceedances decreased for most of locations with large NOx reductions in South Korea and China compared to 2010–2019. The large decreases of the MDA8 ozone exceedances occur in particular at the background sites during spring. In Gosung, Gangwondo (~600 m above sea level), the exceedances drop to ~5 % from 30 % in springtime during the COVID-19 pandemic. The concept of decreases of ozone in the boundary layer in Seoul and Gangwon-do to reductions in the emissions was confirmed by regional model simulations. The reductions of ozone exceedances did not occur at the major cities and provinces during summer of the COVID-19 pandemic with much smaller decreases of NOx in South Korea and China compared to spring. This study demonstrates distinctions between spring and summer in the formation and transport of surface ozone in South Korea and the need of monitoring and modeling with focus on different processes in each season or a finer time scale.

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Reductions in NO₂ concentrations in Seoul, South Korea detected from space and ground-based monitors prior to and during the COVID-19 pandemic

Cited by 7 publications

References 46 publications

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Influence of Aqueous‐Phase Chemistry on the Concentrations of PM_2.5 and Hydrometers During the Development of Convective Clouds Over the Yellow Sea in July of 2017

Changes in surface ozone in South Korea on diurnal to decadal time scale for the period of 2001–2021

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Reductions in NO2 concentrations in Seoul, South Korea detected from space and ground-based monitors prior to and during the COVID-19 pandemic

Cited by 7 publications

References 46 publications

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Influence of Aqueous‐Phase Chemistry on the Concentrations of PM2.5 and Hydrometers During the Development of Convective Clouds Over the Yellow Sea in July of 2017

Changes in surface ozone in South Korea on diurnal to decadal time scale for the period of 2001–2021

Contact Info

Product

Resources

About

Reductions in NO₂ concentrations in Seoul, South Korea detected from space and ground-based monitors prior to and during the COVID-19 pandemic

Influence of Aqueous‐Phase Chemistry on the Concentrations of PM_2.5 and Hydrometers During the Development of Convective Clouds Over the Yellow Sea in July of 2017