This interactive horizon chart visualizes air pollution measurements across Seoul districts, allowing users to compare six pollutants (CO, NO2, O3, PM2.5, PM10, SO2) for selected years (2017–2019) and adjustable band counts. Built with D3 v7 and SVG, it uses `d3.csv` to load data, `d3.schemeBlues` and related color schemes for pollution-specific palettes, and `select` elements with change events to re-render the chart. The SVG dimensions are fixed at 1200×950 pixels, with margins defining the plotting area.