Diurnal variation of aerosol optical depth and PM2.5 in South Korea

A synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model

Elizabeth M. Lennartson, Jun Wang, Juping Gu, Lorena Castro Garcia, Cui Ge, Meng Gao, Myungje Choi, Pablo E. Saide, Gregory R. Carmichael, Jhoon Kim, Scott J. Janz

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET (AErosol RObotic NETwork) sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ (Korea-United States Air Quality) field campaign in May and June of 2016. The extent to which the WRF-Chem (Weather Research and Forecasting coupled with Chemistry) model and the GOCI (Geostationary Ocean Color Imager) satellite retrieval can describe these variations is also analyzed. On a daily average, aerosol optical depth (AOD) at 550;nm is 0.386 and shows a diurnal variation of 20 to-30;% in inland sites, which is larger than the AOD of 0.308 and diurnal variation of ±20;% seen in coastal sites. For all the inland and coastal sites, AERONET, GOCI, and WRF-Chem, and observed PM2.5 (particulate matter with aerodynamic diameter less than 2.5;μm) data generally show dual peaks for both AOD and PM2.5, one in the morning (often at g-1/4 08:00-10:00;KST, Korea Standard Time, especially for PM2.5) and another in the early afternoon ( g-1/4 14:00;KST, albeit for PM2.5 this peak is smaller and sometimes insignificant). In contrast, Ångström exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase in the Ångström exponent from morning to evening, reflecting an overall decrease in particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum requirement of g-1/4 2 years of observation is needed in coastal rural sites, twice as long as that required for the urban sites, which suggests that the diurnal variation of AOD in an urban setting is more distinct and persistent. While Korean GOCI satellite retrievals are able to consistently capture the diurnal variation of AOD (although it has a systematically low bias of 0.04 on average and up to 0.09 in later afternoon hours), WRF-Chem clearly has a deficiency in describing the relative change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Furthermore, the ratio between PM2.5 and AOD in WRF-Chem is persistently larger than the observed counterparts by 30;%-50;% in different sites, but spatially no consistent diurnal variation pattern of this ratio can be found. Overall, the relatively small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the large diurnal variation of AOD-PM2.5 relationships (with the PM2.5;g-•;AOD ratio being largest in the early morning, decreasing around noon, and increasing in late afternoon) and, therefore, the need to use AOD from geostationary satellites to constrain either modeling or estimate of surface PM2.5 for air quality application.

Original languageEnglish
Pages (from-to)15125-15144
Number of pages20
JournalAtmospheric Chemistry and Physics
Volume18
Issue number20
DOIs
Publication statusPublished - 2018 Oct 22

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optical depth
diurnal variation
air quality
aerosol
weather
AERONET
GOCI
aerosol property
geostationary satellite
urban site
climatology
aerodynamics
particulate matter
particle size
spatial distribution

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Lennartson, Elizabeth M. ; Wang, Jun ; Gu, Juping ; Castro Garcia, Lorena ; Ge, Cui ; Gao, Meng ; Choi, Myungje ; Saide, Pablo E. ; Carmichael, Gregory R. ; Kim, Jhoon ; Janz, Scott J. / Diurnal variation of aerosol optical depth and PM2.5 in South Korea : A synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model. In: Atmospheric Chemistry and Physics. 2018 ; Vol. 18, No. 20. pp. 15125-15144.
@article{7f88492f78ae479aac724d50c3aabc31,
title = "Diurnal variation of aerosol optical depth and PM2.5 in South Korea: A synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model",
abstract = "Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET (AErosol RObotic NETwork) sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ (Korea-United States Air Quality) field campaign in May and June of 2016. The extent to which the WRF-Chem (Weather Research and Forecasting coupled with Chemistry) model and the GOCI (Geostationary Ocean Color Imager) satellite retrieval can describe these variations is also analyzed. On a daily average, aerosol optical depth (AOD) at 550;nm is 0.386 and shows a diurnal variation of 20 to-30;{\%} in inland sites, which is larger than the AOD of 0.308 and diurnal variation of ±20;{\%} seen in coastal sites. For all the inland and coastal sites, AERONET, GOCI, and WRF-Chem, and observed PM2.5 (particulate matter with aerodynamic diameter less than 2.5;μm) data generally show dual peaks for both AOD and PM2.5, one in the morning (often at g-1/4 08:00-10:00;KST, Korea Standard Time, especially for PM2.5) and another in the early afternoon ( g-1/4 14:00;KST, albeit for PM2.5 this peak is smaller and sometimes insignificant). In contrast, {\AA}ngstr{\"o}m exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase in the {\AA}ngstr{\"o}m exponent from morning to evening, reflecting an overall decrease in particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum requirement of g-1/4 2 years of observation is needed in coastal rural sites, twice as long as that required for the urban sites, which suggests that the diurnal variation of AOD in an urban setting is more distinct and persistent. While Korean GOCI satellite retrievals are able to consistently capture the diurnal variation of AOD (although it has a systematically low bias of 0.04 on average and up to 0.09 in later afternoon hours), WRF-Chem clearly has a deficiency in describing the relative change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Furthermore, the ratio between PM2.5 and AOD in WRF-Chem is persistently larger than the observed counterparts by 30;{\%}-50;{\%} in different sites, but spatially no consistent diurnal variation pattern of this ratio can be found. Overall, the relatively small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the large diurnal variation of AOD-PM2.5 relationships (with the PM2.5;g-•;AOD ratio being largest in the early morning, decreasing around noon, and increasing in late afternoon) and, therefore, the need to use AOD from geostationary satellites to constrain either modeling or estimate of surface PM2.5 for air quality application.",
author = "Lennartson, {Elizabeth M.} and Jun Wang and Juping Gu and {Castro Garcia}, Lorena and Cui Ge and Meng Gao and Myungje Choi and Saide, {Pablo E.} and Carmichael, {Gregory R.} and Jhoon Kim and Janz, {Scott J.}",
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Diurnal variation of aerosol optical depth and PM2.5 in South Korea : A synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model. / Lennartson, Elizabeth M.; Wang, Jun; Gu, Juping; Castro Garcia, Lorena; Ge, Cui; Gao, Meng; Choi, Myungje; Saide, Pablo E.; Carmichael, Gregory R.; Kim, Jhoon; Janz, Scott J.

In: Atmospheric Chemistry and Physics, Vol. 18, No. 20, 22.10.2018, p. 15125-15144.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Diurnal variation of aerosol optical depth and PM2.5 in South Korea

T2 - A synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model

AU - Lennartson, Elizabeth M.

AU - Wang, Jun

AU - Gu, Juping

AU - Castro Garcia, Lorena

AU - Ge, Cui

AU - Gao, Meng

AU - Choi, Myungje

AU - Saide, Pablo E.

AU - Carmichael, Gregory R.

AU - Kim, Jhoon

AU - Janz, Scott J.

PY - 2018/10/22

Y1 - 2018/10/22

N2 - Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET (AErosol RObotic NETwork) sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ (Korea-United States Air Quality) field campaign in May and June of 2016. The extent to which the WRF-Chem (Weather Research and Forecasting coupled with Chemistry) model and the GOCI (Geostationary Ocean Color Imager) satellite retrieval can describe these variations is also analyzed. On a daily average, aerosol optical depth (AOD) at 550;nm is 0.386 and shows a diurnal variation of 20 to-30;% in inland sites, which is larger than the AOD of 0.308 and diurnal variation of ±20;% seen in coastal sites. For all the inland and coastal sites, AERONET, GOCI, and WRF-Chem, and observed PM2.5 (particulate matter with aerodynamic diameter less than 2.5;μm) data generally show dual peaks for both AOD and PM2.5, one in the morning (often at g-1/4 08:00-10:00;KST, Korea Standard Time, especially for PM2.5) and another in the early afternoon ( g-1/4 14:00;KST, albeit for PM2.5 this peak is smaller and sometimes insignificant). In contrast, Ångström exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase in the Ångström exponent from morning to evening, reflecting an overall decrease in particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum requirement of g-1/4 2 years of observation is needed in coastal rural sites, twice as long as that required for the urban sites, which suggests that the diurnal variation of AOD in an urban setting is more distinct and persistent. While Korean GOCI satellite retrievals are able to consistently capture the diurnal variation of AOD (although it has a systematically low bias of 0.04 on average and up to 0.09 in later afternoon hours), WRF-Chem clearly has a deficiency in describing the relative change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Furthermore, the ratio between PM2.5 and AOD in WRF-Chem is persistently larger than the observed counterparts by 30;%-50;% in different sites, but spatially no consistent diurnal variation pattern of this ratio can be found. Overall, the relatively small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the large diurnal variation of AOD-PM2.5 relationships (with the PM2.5;g-•;AOD ratio being largest in the early morning, decreasing around noon, and increasing in late afternoon) and, therefore, the need to use AOD from geostationary satellites to constrain either modeling or estimate of surface PM2.5 for air quality application.

AB - Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET (AErosol RObotic NETwork) sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ (Korea-United States Air Quality) field campaign in May and June of 2016. The extent to which the WRF-Chem (Weather Research and Forecasting coupled with Chemistry) model and the GOCI (Geostationary Ocean Color Imager) satellite retrieval can describe these variations is also analyzed. On a daily average, aerosol optical depth (AOD) at 550;nm is 0.386 and shows a diurnal variation of 20 to-30;% in inland sites, which is larger than the AOD of 0.308 and diurnal variation of ±20;% seen in coastal sites. For all the inland and coastal sites, AERONET, GOCI, and WRF-Chem, and observed PM2.5 (particulate matter with aerodynamic diameter less than 2.5;μm) data generally show dual peaks for both AOD and PM2.5, one in the morning (often at g-1/4 08:00-10:00;KST, Korea Standard Time, especially for PM2.5) and another in the early afternoon ( g-1/4 14:00;KST, albeit for PM2.5 this peak is smaller and sometimes insignificant). In contrast, Ångström exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase in the Ångström exponent from morning to evening, reflecting an overall decrease in particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum requirement of g-1/4 2 years of observation is needed in coastal rural sites, twice as long as that required for the urban sites, which suggests that the diurnal variation of AOD in an urban setting is more distinct and persistent. While Korean GOCI satellite retrievals are able to consistently capture the diurnal variation of AOD (although it has a systematically low bias of 0.04 on average and up to 0.09 in later afternoon hours), WRF-Chem clearly has a deficiency in describing the relative change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Furthermore, the ratio between PM2.5 and AOD in WRF-Chem is persistently larger than the observed counterparts by 30;%-50;% in different sites, but spatially no consistent diurnal variation pattern of this ratio can be found. Overall, the relatively small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the large diurnal variation of AOD-PM2.5 relationships (with the PM2.5;g-•;AOD ratio being largest in the early morning, decreasing around noon, and increasing in late afternoon) and, therefore, the need to use AOD from geostationary satellites to constrain either modeling or estimate of surface PM2.5 for air quality application.

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