Synoptic circulation factors associated with wintertime high-PM_2.5 concentrations in seoul, Republic of Korea: Their interpretations and applications

Many studies have explored atmospheric circulation fields associated with high particulate matter (PM) events, but only a few studies have evaluated the relative importance of meteorological variables in the circulation fields. In this study, we applied factor analysis method to examine meteorological variables related to the synoptic pattern of high-PM_2.5 episodes (i.e., days with daily averaged PM_2.5 concentration exceeding 35 μg m⁻³) in Seoul, Republic of Korea, during the winter season of 2004–2018. Here, we highlight three independent key factors (F1, F2, and F3) associated with high-PM_2.5 concentrations. F1 is related to temperature (T) and meridional wind (V) at 850 hPa and 1000 hPa (i.e., T850, T1000, V850, and V1000) and temperature and geopotential height (Z) at 500 hPa (i.e., T500 and Z500). It is the most strongly correlated with T850, indicating an increase in thermal stability over Korea during high-PM_2.5 events due to vertically reduced atmospheric ventilation. Meanwhile, F2 is significantly related to the geopotential height and zonal wind (U) at 850 hPa and 1000 hPa (i.e., Z850, Z1000, U850, and U1000). This indicates a dynamically stable condition due to the anomalous easterlies caused by the vertically elongated anticyclone over the northern part of the Korean Peninsula. Finally, F3 is positively associated with zonal and meridional winds at 500 hPa (i.e., U500 and V500). This means that relatively strong winds in the low-to-mid troposphere contribute to high-PM_2.5 concentrations by transporting pollutants from the industrial regions of eastern China to Korea. We also examined the possible influence of climate change on high-PM_2.5 concentrations based on the aforementioned three factors. According to the various shared socioeconomic pathway (SSP) scenarios, F1 increases significantly for all SSP scenarios compared to F2 and F3, indicating that synoptic patterns related to F1 occur frequently, leading to a favorable condition for high-PM_2.5 concentrations. Thus, our finding suggests that climate change alone could worsen air quality in the future even without changes in direct PM_2.5 emissions.