This study investigates how long-term changes in mesoscale wind systems have influenced near-surface PM10 concentrations in central Korea, focusing on Chungcheongbuk-do (Chungbuk Province) during spring from 2000 to 2024. Observational data reveal a nationwide decline in near-surface wind speeds, particularly during spring in the 2010s. Empirical Orthogonal Function (EOF) analysis of 850 hPa wind speed anomalies indicates that this weakening trend is linked to synoptic-scale atmospheric variability over the East Asia-North Pacific region. As transboundary contributions of PM10, particularly from eastern China, have declined in recent years, the role of mesoscale wind patterns in shaping local PM10 concentrations in central Korea has become increasingly significant. To assess the influence of weakened mesoscale winds, two contrasting years were analyzed: 2011, marked by anomalously strong winds, and 2023, characterized by anomalously weak winds. Eulerian PM10 flux convergence (PMFC) analysis revealed a shift from divergence-driven dispersion in 2011 to weak PM10 convergence and accumulation in 2023. Despite these stagnant conditions in 2023, PM10 concentrations continued to decline in both Chungbuk and across Korea, underscoring the dominant effect of anthropogenic emission reductions. These findings suggest that although weakened wind conditions can limit pollutant dispersion, sustained emission control measures remain effective in improving air quality.

A novel PM (powder metallurgy) steel for automotive power-train gear components was developed to reduce manufacturing cost, while meeting application requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out and compared to conventional forged steel. Pinion gears for auto-transmission were also manufactured by helical pressing, sintering, and surface densification process. In order to evaluate the durability of the PM parts, auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable tensile, bending fatigue, contact fatigue strengths and improved gear tooth profile. The PM gears also showed good performance during the transmission durability tests. As a result, the PM gears showed significant potential to replace the conventional forged steel gears manufactured by tooth machining (hobbing, shaving, and grinding) processes.

In this study, surface particulate matter (PM2.5) concentrations were calculated based on empirical equations using measurements of ceilometer backscatter intensities and meteorological variables taken over 19 months. To quantify the importance of meteorological conditions on the calculations of surface PM2.5 concentrations, eight different meteorological conditions were considered. For each meteorological condition, the optimal upper limit height for an integration of ceilometer backscatter intensity and coefficients for the empirical equations were determined using cross-validation processes with and without considering meteorological variables. The results showed that the optimal upper limit heights and coefficients depended heavily on the meteorological conditions, which, in turn, exhibited extensive impacts on the estimated surface PM2.5 concentrations. A comparison with the measurements of surface PM2.5 concentrations showed that the calculated surface PM2.5 concentrations exhibited better results (i.e., higher correlation coefficient and lower root mean square error) when considering meteorological variables for all eight meteorological conditions. Furthermore, applying optimal upper limit heights for different weather conditions revealed better results compared with a constant upper limit height (e.g., 150 m) that was used in previous studies. The impacts of vertical distributions of ceilometer backscatter intensities on the calculations of surface PM2.5 concentrations were also examined.