Analysis of aerosol properties at recent (2015-2018) high concentration events

Department of Urban and Environmental Engineering (Disaster Management Engineering)This research has been done to find out unique physical, chemical, and optical characteristics of aerosols in the case of high PM concentration events over the East Asian region, especially in Korea and China, by using various observations measured during recent four years. To analyze those characteristics of aerosols as high concentration events occur, various measurement data are used, like ambient surface air monitoring data (for physical properties) from national network in both Korea and China, Intensive Monitoring Data (for chemical properties), AERONET, GOCI satellite (for optical properties), and meteorological data during recent years (2015 ??? 2018). It is found that concentrations of PM2.5 in China has rapidly decreased because of stringent air pollution control policies by the Chinese government, ???Air Pollution Prevention and Control Action Plan???. However, in Korea, the PM2.5 concentrations of HCD (high concentration days) and the outliers of PM2.5 concentrations shows increasing trend by the year. In particular, in Ulsan, where is the representative industrial city, high concentrations of PM2.5 are shown during summer because a significant amount of VOCs emitted from the petrochemical industry will be converted into secondary aerosols through photochemical formation with strong solar insolation. By using statistical significant test, we found that the synoptic condition in winter season is important for long-range transport at Seoul metropolitan region, while as for Ulsan at the bay area, the local circulation is important in summer. In the case of chemical property, NO3- is dominant in winter season at megacities (Seoul, Beijing) due to a large amount of NOx emitted from numerous mobile sources and NO3- is well formed in low temperature. SO42- is actively produced in industrial areas (Ulsan) where emit a large amount of SO2 and VOCs, and these components form SO42- through active photochemical reactions with strong solar energy during summer. In Beijing, the highest OC concentration during autumn and winter is mainly due to the intensive emission of OC from coal combustion for residential winter heating. The optical characteristics are analyzed by using ground based remote sensing data and satellite image. It is obvious that the aerosols caused by natural sources were dominant in section of coarse mode, and those secondary aerosols formed through chemical reaction with anthropogenic emission were in fine mode. This study provides with observational evidences to confirm that each different region has different physical, chemical and optical characteristics of aerosol with different time period. The comprehensive results analyzed from this study and integrated methodologies suggested in this study might be useful to make better in-depth understanding of the relations between various aerosol properties in certain region and period.clos

New Era of Air Quality Monitoring from Space: Geostationary Environment Monitoring Spectrometer (GEMS)

GEMS will monitor air quality over Asia at unprecedented spatial and temporal resolution from GEO for the first time, providing column measurements of aerosol, ozone and their precursors (nitrogen dioxide, sulfur dioxide and formaldehyde). Geostationary Environment Monitoring Spectrometer (GEMS) is scheduled for launch in late 2019 - early 2020 to monitor Air Quality (AQ) at an unprecedented spatial and temporal resolution from a Geostationary Earth Orbit (GEO) for the first time. With the development of UV-visible spectrometers at sub-nm spectral resolution and sophisticated retrieval algorithms, estimates of the column amounts of atmospheric pollutants (O3, NO2, SO2, HCHO, CHOCHO and aerosols) can be obtained. To date, all the UV-visible satellite missions monitoring air quality have been in Low Earth orbit (LEO), allowing one to two observations per day. With UV-visible instruments on GEO platforms, the diurnal variations of these pollutants can now be determined. Details of the GEMS mission are presented, including instrumentation, scientific algorithms, predicted performance, and applications for air quality forecasts through data assimilation. GEMS will be onboard the GEO-KOMPSAT-2 satellite series, which also hosts the Advanced Meteorological Imager (AMI) and Geostationary Ocean Color Imager (GOCI)-2. These three instruments will provide synergistic science products to better understand air quality, meteorology, the long-range transport of air pollutants, emission source distributions, and chemical processes. Faster sampling rates at higher spatial resolution will increase the probability of finding cloud-free pixels, leading to more observations of aerosols and trace gases than is possible from LEO. GEMS will be joined by NASA's TEMPO and ESA's Sentinel-4 to form a GEO AQ satellite constellation in early 2020s, coordinated by the Committee on Earth Observation Satellites (CEOS)

Factors affecting recent PM2.5 concentrations in China and South Korea from 2016 to 2020

This study used observational data and a chemical transport model to investigate the contributions of several factors to the recent change in air quality in China and South Korea from 2016 to 2020. We focused on observational data analysis, which could reflect the annual trend of emission reduction and adjust existing emission amounts to apply it into a chemical transport model. The observation data showed that the particulate matter (PM2.5) concentrations during winter 2020 decreased by ???23.4???% (???14.68?????g/m3) and?????????19.5???% (???5.73?????g/m3) in China and South Korea respectively, compared with that during winter 2016. Meteorological changes, the existing national plan for a long-term emission reduction target, and unexpected events (i.e., Coronavirus disease 2019 (COVID-19) in China and South Korea and the newly introduced special winter countermeasures in South Korea from 2020) are considered major factors that may affect the recent change in air quality. The impact of different meteorological conditions on PM2.5 concentrations was assessed by conducting model simulations by fixing the emission amounts; the results indicated changes of +7.6???% (+4.77?????g/m3) and???+???9.7???% (+2.87?????g/m3) in China and South Korea, respectively, during winter 2020 compared to that during winter 2016. Due to the existing and pre-defined long-term emission control policies implemented in both countries, PM2.5 concentration significantly decreased from winter 2016???2020 in China (???26.0???%; ???16.32?????g/m3) and South Korea (???9.1???%; ???2.69?????g/m3). The unexpected COVID-19 outbreak caused the PM2.5 concentrations in China to decrease during winter 2020 by another ???5.0???% (???3.13?????g/m3). In South Korea, the winter season special reduction policy, which was introduced and implemented in winter 2020, and the COVID-19 pandemic may have contributed to ???19.5???% (???5.92?????g/m3) decrease in PM2.5 concentrations

Networking in-situ ground measurements for validation of Korean GEMS (Geostationary Environmental Monitoring Satellite/Spectrometer) products

Considering that geostationary environment satellites (GEO) will be launched simultaneously in Korea (GEMS), the United States (TEMPO) and Europe (Sentinel-4) with the time frame of from 2019 to 2021, it is a very challenging research task to establish the validation strategy of GEO L2 products and to integrate in-situ ground measurements by making the linkage with each other. This work might be one of very important tasks that determines the success or failure of the development project for GEO because maintaining the high accuracy and consistency of its products is critical to achieve the scientific goals of the entire satellite development project. To evaluate the products of Korean GEMS, the GEMS Science Team will utilize the surface air quality monitoring data at more than 500 ground stations, the chemical composition information at 6 Supersites, the remote sensing data from Korean LIDAR network, the intensive aircraft campaign data, i.e. KORUS-AQ 2016 data and MAPS-SEOUL 2015 data within the Korean Peninsula. In addition, several ground measurement and remote sensing data over East Asia including China and Japan, for example, the MAX-DOAS network, NASA???s PANDORA network and AERONET network, EANET data and WMO Global Atmospheric ozone monitoring data will also be used. Moreover, current operated LEO environmental satellite data can be also valuable for comparison to GEMS data

Role of Salts in Phase Transformation of Clathrate Hydrates under Brine Environments

Although ion exclusion is a naturally occurring and commonly observed phenomenon in clathrate hydrates, an understanding for the effect of salt ions on the stability of clathrate hydrates is still unclear. Here we report the first observation of phase transformation of structure I and structure II clathrate hydrates using solid-state ¹³C, ¹⁹F, and ²³Na magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, combined with X-ray diffraction and Raman spectroscopy. The phase transformation of clathrate hydrates in salt environments is found to be closely associated with the quadruple point of clathrate hydrate/hydrated salts and the eutectic point of ice/hydrated salts. The formation of the quasi-brine layer (QBL) is triggered at temperatures a little lower than the eutectic point, where an increasing salinity and QBL does not affect the stability of clathrate hydrates. However, at temperatures above the eutectic point, all hydrated salts and the QBL melt completely to form brine solutions, destabilizing the clathrate hydrate structures. Temperature-dependent in situ NMR spectroscopy under pressure also allows us to directly detect the quadruple point of clathrate hydrates in salt environments, which has been determined only by visual observations

Enhanced Hydrogen-Storage Capacity and Structural Stability of an Organic Clathrate Structure with Fullerene (C₆₀) Guests and Lithium Doping

An effective combination of host and guest molecules in a framework type of architecture can enhance the structural stability and physical properties of clathrate compounds. We report here that an organic clathrate compound consisting of a fullerene (C₆₀) guest and a hydroquinone (HQ) host framework shows enhanced hydrogen-storage capacity and good structural stability under pressures and temperatures up to 10 GPa and 438 K, respectively. This combined structure is formed in the extended β-type HQ clathrate and admits 16 hydrogen molecules per cage, leading to a volumetric hydrogen uptake of 49.5 g L^–1 at 77 K and 8 MPa, a value enhanced by 130% compared to that associated with the β-type HQ clathrate. A close examination according to density functional theory calculations and grand canonical Monte Carlo simulations confirms the synergistic combination effect of the guest–host molecules tailored for enhanced hydrogen storage. Moreover, the model simulations demonstrate that the lithium-doped HQ clathrates with C₆₀ guests reveal exceptionally high hydrogen-storage capacities. These results provide a new playground for additional fundamental studies of the structure–property relationships and migration characteristics of small molecules in nanostructured materials