Using Visibility to Estimate PM2.5 Concentration Trends in Seoul and Chuncheon from 1982 to 2014

Long-term trend analysis on air pollutant concentrations is very important to diagnose the present status and plan for the future. In this study, the long-term trends of PM2.5 concentrations were estimated based on the relationship between the visibility and PM2.5 concentration regarding the effects of relative humidity in Seoul and Chuncheon. The relationships between the visibility and PM2.5 concentration were derived from the measurement data in 2015 and 2016. Then, the annual trends of PM2.5 concentration from 1982 to 2014 were estimated and compared to those of PM10 concentration available in Seoul and Chuncheon. During the estimation process, four ranges of relative humidity were considered such as less than 30%, 31 similar to 50%, 51 similar to 70%, and 71 similar to 90%. In Seoul and Chuncheon, the visibility and PM2.5 concentration generally have the inverse relationship while the visibility decreases as the relative humidity increases. The estimated PM2.5 concentrations similarly showed the decreasing tendencies from 2006 to 2012 in Seoul and Chuncheon. However, the estimated PM2.5 concentrations showed the increasing tendency before 2005 in Chuncheon in contrast to the decreasing tendency in Seoul. This implies that the long-term trends of PM2.5 concentration in different cities in South Korea reflect the local influencing factors. For example, 'Special Act on the Improvement of Atmospheric Environment in the Seoul Metropolitan Area' can affect the different long-term trends in Seoul and Chuncheon. The estimated PM2.5 concentrations were validated with the measured ones in Seoul and Chuncheon. While the general tendencies were well matched between the estimated and measured concentrations, the PM2.5 concentration trends in 1990s and their monthly variations are needed to be improved quantitatively using more reference data for longer years.