1. Jeong_et_al2.jpg
    Title
    Future projections of winter haze events in northern East Asia under different SSPs
    Authors
    Jaein I. Jeong, Rokjin J. Park, Sang-Wook Yeh
    Picture caption
    Relationship between the Haze Weather Index (HWI) and observed PM2.5 anomalies, showing stronger wintertime PM2.5 increases with higher HWI, together with projected increases in potential haze days by the 2090s under different SSP scenarios.
    Summary
    This study examines how climate change may affect winter haze in northern East Asia using the Haze Weather Index. Analysis of observational data shows strong links between atmospheric stagnation and PM2.5 levels. Climate projections indicate haze-favorable conditions could increase substantially by 2100, with severe events rising up to 87% under high-emission scenarios. Temperature-driven stagnation is the main driver, suggesting climate change may undermine air quality improvements despite emission reductions.
    1. Ha_et_al.png
    Title
    First evaluation of the GEMS glyoxal products against TROPOMI and ground-based measurements
    Authors
    Ha, E. S., Park, R. J., Kwon, H.-A., Lee, G. T., Lee, S. D., Shin, S., Lee, D.-W., Hong, H. et al.
    Picture caption
    Difference of GEMS glyoxal VCDs according to the reference sector. Comparison of the seasonal variation of GEMS and TROPOMI glyoxal VCDs, with and without NO2 correction.
    Summary
    In this study, we evaluated the GEMS glyoxal products by comparing them with TROPOMI and MAX-DOAS measurements. GEMS and TROPOMI VCDs present similar spatial distributions. Monthly variations in GEMS VCDs and TROPOMI and MAX-DOAS VCDs differ in northeastern Asia, which we attributed to a polluted reference spectrum and high NO2 concentrations. GEMS glyoxal products with unparalleled temporal resolution would enrich our understanding of VOC emissions and diurnal variation.
    1. Lee_et_al_GEMS.png
    Title
    First evaluation of the GEMS formaldehyde product against TROPOMI and ground-based column...
    Authors
    Gitaek T. Lee, Rokjin J. Park, Hyeong-Ahn Kwon, Eunjo S. Ha, Sieun D. Lee, Seunga Shin, et al.
    Picture caption
    Validation of GEMS HCHO VCD using TROPOMI and ground-based column measurements (MAX-DOAS, FTIR) in the first year of GEMS deployment
    Summary
    We present the first evaluation of the operational GEMS formaldehyde (HCHO) vertical column densities (VCDs) during and after the in-orbit test (IOT) period (August–October 2020) by comparing them with the products from the TROPOMI, FTIR and MAX-DOAS instruments. During the IOT, the GEMS HCHO VCDs reproduced the observed spatial pattern of TROPOMI VCDs (r = 0.62–0.90) with high biases (10 %–16 %). GEMS HCHO VCDs showed consistent hourly variations with MAX-DOAS (r = 0.77) and FTIR (r = 0.86) but were 30–40 % lower than ground-based observations. Utilizing the averaging kernel smoothing method reduces the low biases by approximately 10 % to 15 %.
    1. Jeong_et_al.jpg
    Title
    Quantitative analysis of winter PM2.5 reduction in South Korea, 2019/20 to 2021/22
    Authors
    Jeong, J.I., Park, R.J., Song, C.-K., Yeh, S.-W., and Woo, J.-H.
    Picture caption
    Factors influencing the decreasing trend of observed winter PM2.5 concentrations over the recent three years, from 2019/20 to 2021/22 in South Korea
    Summary
    Over the past three years (2019/20 to 2021/22), the observed winter PM2.5 concentration in South Korea has decreased by an average of 21.2% (15.9% to 24.2%) compared to the reference year (2018/19). Among the three factors considered, meteorological changes contributed the most to the PM2.5 reduction, with an average of 12.9% (6.8% to 17.3%), followed by a decrease in anthropogenic emissions from China of 5.1% (2.7% to 7.9%) and South Korea of 1.7% (1.3% to 1.9%).
    1. 스크린샷 2026-01-20 11.04.53.png
    Title
    Impact of Recent Meteorological Changes on Surface Ozone Increases in Seoul Metropolitan Area
    Authors
    Haein Lee, Rokjin Park, Jaein Jeong
    Picture caption
    Anomaly of MDA8 ozone concentrations averaged in SMA during the ozone season (left). Trend and contributions of meteorological variables to predicted ozone concentrations in a RF model (right).
    Summary
    This study examines the meteorological drivers behind increasing surface ozone trend using long-term observations and a Random Forest model. We analyzed annual trends of meteorological factors at three Automated Synoptic Observing Systems (ASOS) stations (Seoul, Suwon, Incheon) and observed a steady increase in insolation by 0.8% per year, with less significant changes in temperature and relative humidity. Random Forest model explained 69% of the observed variance in surface ozone, with predictions closely tracking observed median values. Meteorological factors, particularly increasing insolation, were significant drivers of the ozone increase in the SMA.
    1. 스크린샷 2026-01-20 11.15.58.png
    Title
    A mixed layer height parameterization in a 3-D chemical transport model : Implications for gas and..
    Authors
    Hyeonmin Kim, Rokjin J. Park, Song-you Hong, Do-Hyeon Park, Sang-Woo Kim, Yujin J. Oak et al.
    Picture caption
    A veraged diurnal variations of observed PBLH (black), simulated PBLH (blue) from the YSU PBL scheme, and simulated MLH (red).
    Summary
    We propose a parameterization of mixed layer height (MLH) derived from the YSU PBL scheme and thoroughly evaluate it by comparing simulations with various observations. We utilized WRF-GC to simulate gas and aerosol distributions over South Korea during the SIJAQ campaign in 2021. The WRF-GC simulations incorporating the MLH parameterization improved the excessive titration of O3 and the overproduction of HNO3 and NO3- in the model. Consequently, the model performances in gaseous and aerosol simulations showed a better agreement with observations, with changes in normalized mean biases (NMBs) of NOX (from 50 % to -27 %), O3 (from -49 % to -28 %), NO3- (from 126 % to 91 %), NH4+(from 113 % to 85 %), BC (from 322 % to 135 %), and PM2.5 (from 58 % to 28 %).
    1. Kim_et_al.png
    Title
    Effect of nitryl chloride chemistry on air quality in South Korea during the KORUS-AQ campaign
    Authors
    Hyeonmin Kim, Rokjin J. Park, Saewung Kim, Jaein I. Jeong, Daun Jeong, Xiao Fu, Seogju Cho
    Picture caption
    Validation of simulated ClNO2 and evaluation of the impacts of the ClNO2 chemistry on air quality in South Korea
    Summary
    We present a quantitative evaluation of the impact of tropospheric ClNO2 chemistry on air quality in South Korea using extensive observations during the Korea-United States Air Quality (KORUS-AQ) field study and a 3-D chemical transport model (CTM). A comparison between the simulated and observed ClNO2 concentrations during the KORUS-AQ campaign shows that the model captures the observed spatial and temporal variations, including local and transboundary transport of ClNO2 and its precursors. The model simulation highlights that ClNO2 plays a significant role in nighttime NOX chemistry by efficiently converting NO to NO2. In addition, it causes a noticeable acceleration of the NOX-O3 cycle. When averaged over the campaign, adding ClNO2 chemistry into the model leads to an increase of O3 (1.1%), NOX (3.1%), •OH (2.0%), HO2• (0.8%), and Cl• (507.8%) and a decrease of TNO3 (HNO3 + aerosol nitrate, 1.7%).
    1. Jeong_and_Park.png
    Title
    Can climate indices forecast daily variations of wintertime PM2.5 concentrations in East Asia?
    Authors
    Jeong, J.I., and and Park, R.J.
    Picture caption
    Anomalous observed surface PM 2.5 concentrations two to four days after the Siberian high pressure weaken or strengthen
    Summary
    We selected four climate indices that reflected the variability of the Siberian high-pressure system and analyzed their correlation with the daily variability of the observed winter PM2.5 concentrations in China and South Korea over the past six years (2014/15–2019/20). Siberian High Intensity (SHI) and East Asian Winter Monsoon (EAWM) indices were good indicators of daily PM2.5 concentration changes. Two to four days after the daily SHI and EAWM indices exceed the threshold (±1), the daily PM2.5 concentrations in East Asia significantly increased or decreased, up to 40% compared to the mean winter PM2.5 concentrations. The climate indices associated with the Siberian high-pressure system thus potentially effectively forecast the daily PM2.5 concentrations in East Asia within a period of one week.
    1. Lee_et_al.png
    Title
    A New Chemistry Climate Model GRIMs CCM: Model Evaluation of Interactive Chemistry Meteorology...
    Authors
    Seungun Lee, Rokjin J. Park, Song You Hong, Myung Seo Koo, Jaein I. Jeong, et al.
    Picture caption
    Comparisons of the seasonal variation of zonally averaged total column ozone, seasonal cycle of the tropospheric ozone concentration at WOUDC station, and spatial distribution of annual mean PM mass concentration in East Asia, U.S., and Europe.
    Summary
    We describe a new chemistry-climate model, Global/Regional Integrated Model system Chemistry Climate Model (GRIMsCCM), developed by coupling the chemistry modules of the GEOS-Chem chemical transport model to the GRIMs general circulation model. The GRIMs-CCM is driven by meteorological variables simulated by the GRIMs and uses simulated gas and aerosol concentrations to calculate the radiative transfer equations at each time step. The model is evaluated by comparing ozone and aerosol concentrations with respective observations from the surface networks and the satellite datasets.