Cluster analysis of number size distributions of atmospheric aerosols downwind of Seoul, Korea

Abstract:

We analyzed hourly number size distributions, ranged from 10.8 nm to 290.8 nm with 70 channels, obtained from measurements using a scanning mobility particle sizer (SMPS). The measurement site was about 35 km southeast of the center of Seoul, downwind of urban pollution in the prevailing westerlies. The site is located in a horseshoe-shaped forested valley with westward-facing slopes, over which biogenic emissions likely prevail. The measurement period was February 2015 to June 2016, except July to September 2015 during which measurements were not made due to inspection and maintenance of SMPS. By means of the k-means clustering method, five clusters were distinguished, which were designated as regional background, local emissions, traffic, nucleation, and growth. The characteristics of each cluster were examined by comparing the size distribution, hourly occurrences in a day, monthly occurrences over the year, meteorology (temperature, wind direction, wind speed, and relative humidity), and pollutant concentrations (PM₁₀, SO₂, NO₂ and BC).