This visualization shows daily air quality measurements from a Phoenix EPA monitoring site, comparing mean concentrations of four pollutants (NO₂, O₃, SO₂, CO) and an overall AQI value across dates in early January 2000. It renders as a grouped bar chart using D3 v6, with `d3.scaleBand` for the date and pollutant groupings, `d3.scaleLinear` for the y-axis, and `d3.schemeSet2` for categorical colors. Hovering over bars triggers a tooltip via D3’s mouse events. The SVG chart loads data from a CSV file, parsing dates with `d3.timeParse` and formatting axis ticks with `d3.timeFormat`.