This visualization displays daily average concentrations of six pollutants (SO2, NO2, O3, CO, PM10, PM2.5) for multiple station codes in 2019. Each small multiple is a horizon chart built with D3 v6, using `d3.area` to render SVG paths and `d3.rollups` to aggregate measurements by station and date. The interactive charts support zooming via `d3.zoom` and show a tooltip on hover that reveals the exact date and pollutant value. Data comes from a CSV file loaded with `d3.csv`, with districts extracted from address strings.