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We present the ambient ozone and relevant observed trace gas dataset in Seoul, South Korea, during the Megacity Air Pollution Studies (MAPS)-Seoul field campaign from May to June of 2015 (MAPS-Seoul 2015). We observed two distinctive periods, one with higher and the other with lower daytime ozone levels despite mostly clear conditions for both periods. The importance of peroxy radical contributions to excess ozone production is illustrated by the substantial differences in the Leighton constant (Φ) for the two periods. Moreover, higher levels of hydroxyl radical (OH) reactivity (s–1) were observed during the high ozone episode compared to the low ozone episode by as much as ~5 s–1. The contributions of nitrogen oxides (NOx) to OH reactivity become less important than those of volatile organic compounds (VOCs) during the high ozone episode, which suggests the NOx saturated ozone production regime. It was also notable that the biogenic VOC isoprene consistently contributed the most to OH reactivity from among the observed VOCs during the afternoon throughout the whole field campaign. Finally, we ran multiple box model scenarios to evaluate the ozone production rates of three different air mixtures: a high ozone mixture, a low ozone mixture, and a simulation of the regional air quality. The results indicate that the total OH reactivity levels and the relative contributions of VOCs to NOx play critical roles in ozone production rates. The simulated air quality mixture results in lower OH reactivity, causing lower ozone production rates than those calculated for the high ozone mixture, which clearly indicates the need for further improvements in the regional model to accurately simulate ozone precursors in the region. The results of this study suggest that a comprehensive trace gas dataset combined with observations of the OH reactivity enables us to properly diagnose the photochemistry behind ozone pollution, leading to effective ozone abatement policies.

To understand the chemical mechanisms of controlling factors in ozone (O3) formation in early summer in Seoul, a comprehensive study encompassing measurement and modeling was conducted under the Megacity Air Pollution Study-Seoul (MAPS-Seoul) campaign. From May 18 to June 12, 2015, O3 and peroxyacetyl nitrate (PAN) were measured, along with their precursors, including NOx and volatile organic compounds (VOCs), at the Korea Institute of Science and Technology, located in northeast Seoul. VOCs were sampled in a canister twice a day (at 09:30 and 15:00) and analyzed via gas chromatography. The meteorological conditions and chemical regimes of the air masses were clearly distinguished during the study period. In May, NOx concentrations were higher with more pronounced diurnal cycles of precursors and O3 under constant westerly winds. By contrast, stagnant conditions developed in June, which reduced the inflow of primary emissions from the downtown area but increased the influence from the neighboring forest under high temperatures. As a result, the ratio of O3 to odd oxygen was higher in June, indicating a less efficient removal of O3 by NOx. In the same context, the air mass was chemically more aged with a higher NO2/NOx ratio and enhanced OH reactivity of oxygenated and biogenic VOCs in June. The overall measurement results suggest that O3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O3 concentrations are the highest of the year.

South Korea has recently achieved developed country status with the second largest megacity in the world, the Seoul Metropolitan Area (SMA). This study provides insights into future changes in air quality for rapidly emerging megacities in the East Asian region. We present total OH reactivity observations in the SMA conducted at an urban Seoul site (May-June, 2015) and a suburban forest site (Sep, 2015). The total OH reactivity in an urban site during the daytime was observed at similar levels (∼15 s(-1)) to those previously reported from other East Asian megacity studies. Trace gas observations indicate that OH reactivity is largely accounted for by NOX (∼50%) followed by volatile organic compounds (VOCs) (∼35%). Isoprene accounts for a substantial fraction of OH reactivity among the comprehensive VOC observational dataset (25-47%). In general, observed total OH reactivity can be accounted for by the observed trace gas dataset. However, observed total OH reactivity in the suburban forest area cannot be largely accounted for (∼70%) by the trace gas measurements. The importance of biogenic VOC (BVOCs) emissions and oxidations used to evaluate the impacts of East Asian megacity outflows for the regional air quality and climate contexts are highlighted in this study.

PM2.5, a critical air pollutant, requires health-conscious management, with concentrations varying across regions due to diverse sources. This study, conducted in South Korea in 2021, employed the geographically weighted regression model to analyze the spatiotemporal correlations of PM2.5 with O3 and the normalized difference vegetation index (NDVI). Regional differences in the correlation between PM2.5 and O3 were observed, influenced by common precursors (SOx, NOx, and volatile organic compounds (VOCs)), seasonal temperature variations, and solar radiation differences. Notably, PM2.5 and O3 exhibited a heightened regression coefficient in summer, emphasizing the need for specific management targeting VOCs and NO2. The interplay between PM2.5 and NDVI revealed a negative overall impact but a positive effect in the central region of Korea, suggesting vegetation's role in the PM2.5 concentration increase due to atmospheric stagnation caused by mountain ranges. These findings enhance our understanding of PM2.5 distribution mechanisms, highlighting the need for tailored policies in each region for effective concentration reductions. [ABSTRACT FROM AUTHOR]

The impact of crop residue burning in northeastern China on South Korean PM2.5 concentrations was assessed via weather conditions, air quality modeling (AQM), and PM2.5 composition data during two cases exceeding 35 µg·m−3 in November 2015. PM2.5 concentration simulations of Case 1 differed from observations by 3.7–17.6 µg·m−3, overestimating the levels by 6–36%; however, Case 2 varied by 20.0–59.8 µg·m−3 from observations, with a 53–91% underestimation. Case 1 was generally well simulated, whereas the Case 2 simulation failed because the emissions of crop residue burning in northeastern China, as confirmed through satellite analysis (MODIS fires and thermal anomalies) and previous research, were not considered. The portion of organic/elemental carbon ratio during Case 2 was 1.6–2.3 times higher than that of Case 1. These results suggest that it is necessary to consider the effects of crop residue burning in northeast China to establish countermeasures to improve air quality and air quality forecasting in South Korea. [ABSTRACT FROM AUTHOR]

High particulate matter (PM2.5) concentrations have been considered a serious environmental issue in South Korea. Recent studies have focused mostly on metropolitan and industrial cities; however, high PM2.5 episodes have also been frequently observed even in small– and middle-sized cities. Thus, in this study, PM2.5 and its major chemical components were measured in a small residential city with low anthropogenic emissions for 2 years to identify the factors affecting the PM2.5 concentrations. Overall, the average PM2.5 concentration was 29.4 μg m−3: about two times higher than the annual ambient air quality standard value. In winter, when the PM2.5 concentrations were generally higher, relative humidity (RH) was significantly correlated with both PM2.5 mass and the PM2.5/PM10 ratio, suggesting that high RH promoted the formation of secondary PM2.5. In addition, SO42− and NO3− were found to be correlated with both NH4+ and K+ in winter, indicating that biomass burning was an important source in this city. Water-soluble organic carbon (WSOC) was also highly correlated with elemental carbon (EC) and K+ in fall and winter, when the burning of agricultural residues actively occurred. During high concentration episodes, NO3− exhibited the highest increase; nevertheless, other components (e.g., K+ and organic carbon) also significantly increased. [ABSTRACT FROM AUTHOR]

Several studies have focused on Ca and P requirements for pigs. These requirements are estimated from their retention and bone formation. However, modern pig breeds have different responses to dietary Ca and P than traditional breeds, and their requirements are expected to change on an annual basis. Besides individual Ca and P needs, the Ca to P ratio (Ca/P) is an important factor in determining requirements. This study aimed to implement a linear and quadratic regression analysis to estimate Ca and P requirements based on average daily gain (ADG), apparent total tract digestibility (ATTD) of Ca (ATTD-Ca), ATTD of P (ATTD-P), and crude protein (CP) digestibility. Results show that Ca/P had linear and quadratic effects on ADG in the phytase-supplemented (PS) group in both the 6-11 kg and 11-25 kg categories. In the latter category, the CP digestibility was linearly increased in response to increasing Ca/P in the without-phytase (WP) group. In the 25-50 kg category, there was a linear response of ADG and linear and quadratic responses of CP digestibility to Ca/P in the PS group, while a linear and quadratic increase in CP digestibility and a quadratic effect on ATTD-Ca were observed in the WP group. In the 50-75 kg category, Ca/P had significant quadratic effects on ADG in the PS and WP groups, along with significant linear and quadratic effects on ATTD-Ca. In addition, Ca/P had significant quadratic effects on ATTD-P and led to a significant linear and quadratic increase in the CP digestibility in the WP group. In the 75-100 kg category, analysis showed a significant decrease in ATTD-Ca and ATTD-P in the PS and WP groups; in the latter, ATTD-P and ATTD-Ca were linearly decreased by increasing Ca/P. In conclusion, our equations predicted a higher Ca/P in the 6-25 kg bodyweight categories and a lower Ca/P in the 50-100 kg category than that recommended in the literature., Competing Interests: No potential conflict of interest relevant to this article was reported., (© Copyright 2021 Korean Society of Animal Science and Technology.)