Daily variation of PM2.5 and covarying meteorological conditions during wintertime using long-term observation in Seoul

Understanding co-variability between particulate matter (PM) concentration and meteorological conditions could provide insight into how the former varies under given weather conditions and eventually improve its prediction skill. However, relatively short data length of observed PM_2.5 is a challenging issue not limited to Korea. Therefore, in such an analysis PM₁₀, which has reliable observation for more than 30 years, has been widely used as a proxy of fine particles. Also, there are two stations in Seoul, Korea have relatively long-term observed PM_2.5 in the period of 2000-current. As a result, more reliable analysis on the daily variation of PM_2.5 in comparison with PM₁₀ and meteorological conditions is feasible. First, the winter-mean of both PM₁₀ and PM_2.5 showed significant decreasing trends in the period of 2000-2020. Interestingly, decreasing trends of these weakened in the last 10 years with a different rate, resulting in a nearly flat trend of PM_2.5 yet a relatively consistent decreasing trend of PM₁₀ in the period of 2010-2020, suggesting a potential discrepancy in the variability of PM_2.5 and that of PM₁₀. Second, unlike the previously noted difference in long-term trends of seasonal mean values, PM_2.5 and PM₁₀ shared significantly similar daily variabilities if Asian dust cases were removed. In other words, the aforementioned discrepancy in the long-term trend of seasonal mean values of PM_2.5 and PM₁₀ does not affect their daily variation. The covarying patterns of PM_2.5 and meteorological conditions were denoted as a migratory synoptic system. In particular, a migratory anticyclone from northwest China had significant positive correlation patterns with PM_2.5 from two days before and remained stagnant over Korea after two days due to blocking by low pressure over the Northern Pacific. Along with this system, warm temperature anomalies and weak northerlies in the low troposphere were present over Korea, which is a conducive condition for high PM_2.5. On the contrary, Asian dust cases were accompanied by cyclone that extended from arid regions of northern China with corresponding negative temperature anomalies and strengthened northerlies. In short, a migratory synoptic system over Korea is tightly correlated with PM_2.5 daily variations as well as PM₁₀. But once again, Asian dust events could be an important mechanism to differentiate daily variations of PM_2.5 and PM₁₀.