1. GA_jeongEA.PNG
    Title
    Compromised Improvement of Poor Visibility Due to PM Chemical Composition Changes in South Korea
    Authors
    Jeong, J.I., Seo J., and Park, R.J.
    Picture caption
    Change of PM2.5 components has compromised poor visibility improvement
    Summary
    Despite a continuous decrease in the PM concentrations in South Korea, the public generally believes that PM air pollution has worsened over the past years. To explain this disparity, we analyzed the characteristics of recent visibility changes using observations of visibility and PM component data observed in Seoul, South Korea, from 2012 to 2018. Annual mean PM2.5 concentrations in Seoul decreased by −5.1% yr−1 during 2012‒2018, whereas annual mean visibility improved by 2.1% yr−1. We found that a lower improvement in visibility was associated with changes in the PM component. Among the PM components affecting poor visibility, contributions of ammonium nitrate (NH4NO3) significantly increased during 2012‒2018 (from 48% in 2012 to 59% in 2018). Increases in NO3− aerosol concentrations were owing to SOx emission reduction and the resulting decreases in SO42− aerosol concentrations, which led to an increase in NH3 available for additional NH4NO3 production in the atmosphere.
    1. OHR Hompage.png
    Title
    Observed versus simulated OH reactivity during KORUS-AQ campaign
    Authors
    Hyeonmin Kim, Rokjin J. Park, Saewung Kim, William H. Brune, Glenn S. Diskin, Alan Fried...
    Picture caption
    Comparison of total, calculated and simulated OH reactivity with missing OH reactivity between total OH reactivity (tOHR) and calculated/simulated OH reactivity (cOHR/sOHR). Model performance to reproduce observed OH concentrations in the models.
    Summary
    We present a holistic examination of tropospheric OH reactivity (OHR) in South Korea. The observed total OHR (tOHR) averaged in the planetary boundary layer (PBL, <2.0 km) and free troposphere was 5.2 s-1 and 2.0 s-1 during the campaign, respectively. These values were higher than the calculated OHR cOHR, 3.4 s-1, 1.0 s-1) derived from trace-gas observations, indicating missing OHR fractions in the PBL and free troposphere of 35% and 50%, respectively. Simulated OHR (sOHR, 2.7 s-1, 0.8 s-1) was substantially lower than both tOHR and cOHR by as much as 60%. Despite this discrepancy, we found that simulated OH concentrations were comparable with those observed during the campaign because of slow OH recycling rates in the models.
    1. mlh Homepage.png
    Title
    Factors determining the seasonal variation of ozone in South Korea
    Authors
    Hyung-MinLee, Rokjin J.Park
    Picture caption
    Monthly mean ozone with shadings for 1-standard deviation calculated spatially over South Korea for daytime (yellow) and nighttime (green). Contributions from domestic emission sources to monthly mean surface level MDA8 ozone in April and July.
    Summary
    We examine locally controllable (domestic anthropogenic) versus uncontrollable (background) contributions to ozone for 2016. We conducted simulations for winter, spring, summer, and fall. The model reproduces observed ozone, showing correlation coefficients (0.40–0.87) against observations. Except for summer, the background ozone are higher than the seasonal ozone in the model. Ozone in South Korea is determined by regional background contributions with summertime domestic ozone formation. The domestic NOx emissions reduce ozone around cities and hardly increase MDA8 in other regions in spring, but it increases MDA8 across the country in summer. Therefore, NOx reduction can be effective in control of ozone in summer, but it can have rather countereffect in spring.
    1. 그림1.png
    Title
    Evaluation of Secondary Organic Aerosol (SOA) Simulations for Seoul, Korea
    Authors
    Yujin J. Oak, Rokjin J. Park, Duseong S. Jo, Alma Hodzic, Jose L. Jimenez, et al.
    Picture caption
    Observed and simulated SOA/ΔCO ratios versus photochemical age, and comparison of observed and simulated mean OA concentrations in the Seoul Metropolitan Area boundary layer.
    Summary
    We compare four different modeling approaches for simulating secondary organic aerosol (SOA) formation, accounting for a significant fraction of total fine particulate matter concentrations in Seoul, Korea. Using GEOS-Chem, a chemical transport model, we find that current SOA schemes show large variabilities. Including an additional precursor species and further oxidation (i.e., chemical aging) of simulated SOA improves model performance. We also find that a simplified scheme with less computational cost can reproduce observed values but generally shows an overestimation in Seoul, indicating uncertainties in parameterization.
    1. paper.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.
    1. GA.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.