Taehyoung Lee

Sea spray aerosol as a unique source of ice nucleating particles

Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratory-generated SSA, when normalized to typical total aerosol number concentrations in the marine boundary layer, agree well with measurements from diverse regions over the oceans. Data in the present study are also in accord with previously published INP measurements made over remote ocean regions. INP number concentrations active within liquid water droplets increase exponentially in number with a decrease in temperature below 0 °C, averaging an order of magnitude increase per 5 °C interval. The plausibility of a strong increase in SSA INP emissions in association with phytoplankton blooms is also shown in laboratory simulations. Nevertheless, INP number concentrations, or active site densities approximated using “dry” geometric SSA surface areas, are a few orders of magnitude lower than corresponding concentrations or site densities in the surface boundary layer over continental regions. These findings have important implications for cloud radiative forcing and precipitation within low-level and midlevel marine clouds unaffected by continental INP sources, such as may occur over the Southern Ocean.

One-pot solvothermal synthesis of magnetic SnFe2O4 nanoparticles and their performance in the photocatalytic degradation of chlortetracycline with visible light radiation

Highly crystalline SnFe2O4 nanoparticles with high saturation magnetization and superior chlortetracycline (CTC) degradation efficiency was developed using a one-pot solvothermal method. The SnFe2O4 nanoparticles about 50 nm were prepared with a simple and cost-effective process performed at 200 °C. Superparamagnetism was observed from the SnFe2O4 nanoparticles with a high saturation magnetization of 74.3 emu g−1. The excellent photocatalytic activity of the SnFe2O4 nanoparticles was demonstrated through the high degradation efficiency of CTC under a visible light/SnFe2O4/9 mM H2O2 process. The effective degradation of CTC with the SnFe2O4 nanoparticles was attributed to the effective absorption of the visible light and the good separation ability of the electron–hole pairs. The synergy effect between SnFe2O4 and H2O2 was analysed, and the optimum initial concentration of H2O2 was determined to be 9 mM to achieve the best photocatalytic result on CTC. The SnFe2O4 nanoparticles also exhibited a fast and easy magnetic retrieval and a stable performance with continuous recycled usage.

Magnetically separable sulfur-doped SnFe2O4/graphene nanohybrids for effective photocatalytic purification of wastewater under visible light

In this report, magnetically recoverable sulfur-doped SnFe2O4/graphene (S-SFO/GR) nanohybrids have been successfully developed via a facile solvothermal method. The characterizations on the structural, morphology, and optical properties of the nanohybrids indicate that S-SFO particles are successfully embedded on the GR nanosheets. The photocatalytic activity has been evaluated by photocatalytic degradation of chlorotetracycline under visible light irradiation. Among the composites with various mass ratios, the quasi-first-order rate constant of the nanohybrids formed with 9wt% S in SFO and 15wt% GR (9S-SFO/GR-15) can reach as high as 1.83min-1, which is much higher than that of SFO (0.68min-1) and SFO/GR (0.91min-1), confirming the important role of S and GR for the photocatalytic process. The combination of the three components of S, SFO, and GR has enhanced the visible light absorption capability and inhibited the recombination of photogenerated electron-hole. The 9S-SFO/GR-15 nanohybrids can be recovered easily by a magnet and reused for five times with remained photocatalytic efficiency about 70%. A possible catalytic mechanism explaining the efficient photocatalytic performances of the prepared nanohybrids has been proposed.

Evaluation of the new capture vaporizer for Aerosol Mass Spectrometers: Characterization of organic aerosol mass spectra

ABSTRACT The Aerosol Mass Spectrometer (AMS) and Aerosol Chemical Speciation Monitor (ACSM) are widely used for quantifying submicron aerosol mass concentration and composition, in particular for organic aerosols (OA). Using the standard vaporizer (SV) installed in almost all commercial instruments, a collection efficiency (CE) correction, varying with aerosol phase and chemical composition, is needed to account for particle bounce losses. Recently, a new “capture vaporizer” (CV) has been shown to achieve CE∼1 for ambient aerosols, but its chemical detection properties show some differences from the SV due to the increased residence time of particles and vaporized molecules inside the CV. This study reports on the properties and changes of mass spectra of OA in CV-AMS using both AMS and ACSM for the first time. Compared with SV spectra, larger molecular-weight fragments tend to shift toward smaller ions in the CV due to additional thermal decomposition arising from increased residence time and hot surface collisions. Artifact CO+ ions (and to a lesser extent, H2O+), when sampling long chain alkane/alkene-like OA (e.g., squalene) in the CV during the laboratory studies, are observed, probably caused by chemical reactions between sampled OA and molybdenum oxides on the vaporizer surfaces (with the carbon derived from the incident OA). No evidence for such CO+ enhancement is observed for ambient OA. Tracer ion marker fractions (fm/z =, i.e., the ratio of the organic signal at a given m/z to the total OA signal), which are used to characterize the impact of different sources are still present and usable in the CV. A public, web-based spectral database for mass spectra from CV-AMS has been established. Copyright

Relationship between reactive oxygen species and water-soluble organic compounds: Time-resolved benzene carboxylic acids measurement in the coastal area during the KORUS-AQ campaign

This study investigated the relationship between water-soluble organic compounds of ambient particulate matter (PM) and cellular redox activity collected from May 28 to June 20 of 2016xa0at the west coastal site in the Republic of Korea during the KORea-US Air Quality (KORUS-AQ) campaign. Automatic four-hour integrated samples operated at a flow rate of 92xa0L per minute for the analysis of organic carbon (OC), water-soluble organic carbon (WSOC), elemental carbon (EC), water-soluble ions (WSIs), and benzene carboxylic acids (BCAs) were collected on a 47xa0mm quartz fiber filter. The influence of atmospheric transport processes was assessed by the Weather Research and Forecasting (WRF) model. OC, EC, WSOC, and BCA were determined by SUNET carbon analyzer, total organic carbon (TOC) analyzer, and liquid chromatography-mass spectrometry mass spectrometry (LC-MSMS), respectively. Twenty-four-hour integrated samples were collected for reactive oxygen species (ROS) analysis using a fluorogenic cell-based method to investigate the main chemical classes of toxicity. The results illustrate that WSOC and specific water-soluble species are associated with the oxidative potential of particulate matter. Pairwise correlation scatterplots between the daily-averaged WSOC and ROS (r2 of 0.81), and 135-BCA and ROS (r2 of 0.84), indicate that secondary organic aerosol production was highly associated with ROS activity. In addition, X-ray spectral analysis together with secondary electron images (SEIs) of PM2.5 particles collected during high ROS concentration events clearly indicate that water-soluble organic aerosols are major contributors to PM2.5 mass. This study provides insight into the components of particulate matter that are drivers of the oxidative potential of atmospheric particulate matter and potential tracers for this activity.

Physicochemical Characteristics of Particulate Matter Emissions of Different Vehicles` Fuel Types

The physicochemical characteristics of particulate matter emissions from various vehicle’s fuel types were studied at the facility of Transport Pollution Research Center (TPRC), National Institute of Environmental Research (NIER), Korea. Three different types of fuels such as gasoline, liquefied petroleum gas (LPG) and diesel were tested on the NIER driving mode and the constant speed modes (30, 70, and 110 km/h). Chemical composition of submicron particles from vehicle emissions was measured by the High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during running cycles. Organics were dominant chemical species of particulate matter emissions for all three different vehicles’ fuel types. Moreover, regardless of fuel types, emission rate of organics and inorganics decreased as the average speed of vehicle increased. The portion of fully oxidized fragment families of CxHyOz accounted for over 98% of organic aerosol (OA) in LPG and diesel vehicles, while the relatively high fraction of CxHy in OA was observed in gasoline vehicle.

Comparison of Real Time Water Soluble Organic Carbon Measurements by Two PILS-TOC Analyzers

Da-Jeong Park, Seokwon Kang, Taehyoung Lee, Hye-Jung Shin, Zang-Ho Shon and Min-Suk Bae* Department of Environmental Engineering, Mokpo National University Environmental Analysis Center, Gwangju Institute of Science and Technology Department of Environmental Science, Hankuk University of Foreign Studies Air Quality Research Division, National Institute of Environmental Research Department of Environmental Engineering, Dong-Eui University