In this study, the contributions of emissions (foreign and domestic) and atmospheric physical and chemical processes to PM2.5 concentrations were evaluated during a high PM2.5 episode (March 24-26, 2018) observed on the Jeju Island in the spring of 2018. These analyses were performed using the community multi-scale air quality (CMAQ) modeling system using the brute-force method and integrated process rate (IPR) analysis, respectively. The contributions of domestic emissions from South Korea (41-45%) to PM2.5 on the Jeju Island were lower than those (81-89%) of long-range transport (LRT) from China. The substantial contribution of LRT was also confirmed in conjunction with the air mass trajectory analysis, indicating that the frequency of airflow from China (58-62% of all trajectories) was higher than from other regions (28-32%) (e.g., South Korea). These results imply that compared to domestic emissions, emissions from China have a stronger impact than domestic emissions on the high PM2.5 concentrations in the study area. From the IPR analysis, horizontal transport contributed substantially to PM2.5 concentrations were dominant in most of the areas of the Jeju Island during the high PM2.5 episode, while the aerosol process and vertical transport in the southern areas largely contributed to higher PM2.5 concentrations.

Temporal and spatial characteristics of the frequency of several weather types and the change in air pollutant concentrations according to these weather types were analyzed over a decade (2007-2016) in seven major cities and a remote area in Korea. This analysis was performed using hourly (or daily) observed data of weather types (e.g., mist, haze, fog, precipitation, dust, and thunder and lighting) and air pollutant criteria (PM10, PM2.5, O3, NO2, CO, and SO2). Overall, the most frequent weather type across all areas during the study period was found to be mist (39%), followed by precipitation (35%), haze (17%), and the other types (≤ 4%). In terms of regional frequency distributions, the highest frequency of haze (26%) was in Seoul (especially during winter and May-June), possibly due to the high population and air pollutant emission sources, while that of precipitation (47%) was in Jeju (summer and winter), due to its geographic location with the sea on four sides and a very high mountain. PM10 concentrations for dust and haze were significantly higher in three cities (up to 250 μg/m3 for dust in Incheon), whereas those for the other four types were relatively lower. The concentrations of PM2.5 and its major precursor gases (NO2 and SO2) were higher (up to 69 μg/m3, 48 ppb, and 16 ppb, respectively, for haze in Incheon) for haze and/or dust than for the other weather types. On the other hand, there were no distinct differences in the concentrations of O3 and CO for the weather types. The overall results of this study confirm that the frequency of weather types and the related air quality depend on the geographic and environmental characteristics of the target areas.

The classification of airflow patterns during high ozone (O3) and PM10 episodes on Jeju Island in recent years (2009-2015), as well as their correlation with meteorological conditions according to classified airflow patterns were investigated in this study. The airflow patterns for O3 and PM10 were classified into four types (Types A-D) and three types (Types E-G), respectively, using the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and synoptic weather charts. Type A was the most dominant airflow pattern for O3 episodes, being characterized by the transport of airflows from urban and industrial areas in China with the highest frequency (about 69%, with a mean of 67 ppb). With regard to the PM10 episodes, Type E was the most dominant airflow pattern, and was mostly associated with long distance transport from Asian dust source regions along northwesterly winds, having the highest frequency (about 92%, with a mean of 136 μg/m3). The variations in the concentration of O3 and PM10 during the study period were clarified in correlation with two pollutant and meteorological variables; for example, the high (low) O3 and PM10 concentrations with high (low) air temperature and/or wind speed and vice versa for precipitation. The contribution of long-range transport to the observed PM10 levels in urban sites for different airflow patterns (Types E-F), if estimated in comparison to the data from the Gosan background site, was found to account for approximately 87-93% (on average) of its input. The overall results of the present study suggest that the variations in O3 and PM10 concentrations on Jeju Island are mainly influenced by the transport effect, as well as the contribution of local emissions.

Long-term variations of PM10 and the characteristics of local meteorology related to its concentration changes were analyzed at 4 air quality sites (Ido-dong, Yeon-dong, Donghong-dong, and Gosan) in Jeju during two different periods, such as PI (2001-2006) and PII (2007-2013), over a 13-year period. Overall, the long-term trend of PM10 was very slightly downward during the whole study period, while the high PM10 concentrations in PII were observed more frequently than those in PI. The concentration variations of PM10 during the study period was clarified in correlation between PM10 and meteorological variables, e.g. the low (high) PM10 concentration with large (small) precipitation or high (low) radiation and in part high PM10 concentrations (especially, Donghong-dong and Gosan) with strong wind speed and the westerly/northwesterly winds. This was likely to be caused by the transport effect (from the polluted regions of China) rather than the contribution of local emission sources. The PM10 concentrations in “Asian dust” and “Haze” weather types were higher, whereas those in “Precipitation”, “Fog”, and “Thunder and Lighting” weather types were lower. The contribution of long-range transport to the observed PM10 levels in the urban center (Ido-dong, Yeon-dong, and Donghong-dong), if estimated by comparison to the data of the background site (Gosan), was found to explain about 80% (on average) of its input.

The characteristics of meteorological conditions related to changes in atmospheric environment on Jeju Island were investigated during recent years (2010-2012). This analysis was performed using the hourly observed data of meteorological variables (air temperature, wind speed and direction) and air pollutants (O3, PM10, SO2, NO2, and CO). Out of 5 pollutants, O3 and PM10 concentrations have frequently exceeded national environmental standards in the study area during the study period, with relatively higher concentrations than the others. The concentrations of O3 and PM10 in 2010 and 2011 were somewhat higher than those in 2012, and their highest concentrations were mostly observed in spring followed by fall. Nighttime O3 concentrations (with relatively high concentration levels) were almost similar to its daytime concentrations, due to less O3 titration by very low NO concentrations in the target area and in part to O3 increase resulting from atmospheric transport processes. The transport effect related to the concentration variations of O3 and PM10 was also clarified in correlation between these pollutants and meteorological variables, e.g. the high exceedance frequency of concentration criteria with strong wind speed and the high concentrations with the westerly/northwesterly winds (e.g., transport from the polluted regions of China). The overall results of this study suggest that the changes in atmospheric environment in the study area were likely to be caused by the transport effect (horizontal and vertical) due to the meteorological conditions rather than the contribution of local emission sources.