Compromised Improvement of Poor Visibility Due to PM Chemical Composition Changes in South Korea

Fine particulate matter (PM) significantly affects visibility, a sensitive indicator of air pollution. Despite continuous decrease in the PM concentrations South Korea, public generally believes that pollution has worsened over past years. To explain this disparity, we analyzed characteristics recent visibility changes using observations and component data observed Seoul, from 2012 to 2018. A significant negative correlation (R = −0.96) existed between PM, with an aerodynamic diameter ≤ 2.5 μm (PM2.5); high PM2.5 concentration was most important contributor poor visibility. Annual mean Seoul decreased by −5.1% yr−1 during 2012–2018, whereas annual improved 2.1% yr−1. We found lower improvement associated component. Among components affecting contributions ammonium nitrate (NH4NO3) increased 2012–2018 (from 48% 59% 2018). Increases NO3− aerosol were owing SOx emission reduction resulting decreases SO42− concentrations, which led increase NH3 available for additional NH4NO3 production atmosphere. change compromised improvement; thus, need be reduced.