This visualization combines a bubble map of 2021 Air Quality Index (AQI) data across the United States with an interactive date histogram, linked through brushing. The map projects data points using `d3.geoAlbersUsa` and `d3.geoPath`, with circle colors mapped via `d3.scaleQuantile` to a scale of AQI ranges. The histogram aggregates data by month with `d3.histogram` and `d3.scaleTime`, displaying mean AQI values. Users can brush a time range (via `d3.brushX`), which filters the map to show only the selected period using React state and `d3.csv`-loaded US EPA data.