This interactive visualization displays Air Quality Index (AQI) data across the United States in 2021, combining a bubble map with a linked histogram. Users can brush over the time-series histogram to filter which data points appear on the map. The map uses d3.geoAlbersUsa and d3.geoPath to render state boundaries, while colored circles indicate AQI values using d3.scaleQuantile. The histogram is built with d3.bin and d3.brushX, with data loaded from a CSV file containing ozone measurements.