This interactive visualization presents daily AQI measurements across U.S. states on a choropleth map, where each state’s fill color reflects its average AQI using a quantile color scale. A linked date histogram below enables brushing to filter the map to a selected time range, with the map updating to show only those states’ data. Built with React and D3 v5, it uses `d3.geoAlbersUsa` and `d3.geoPath` for map projection, `d3.scaleQuantile` for coloring, and `d3.brushX` for interactive selection. The data comes from a CSV file loaded via `d3.csv`.