This visualization shows daily air pollution trends for four pollutants—NO2, O3, SO2, and CO—in Phoenix, Arizona, using data from January 2000. Multiple time-series lines are drawn in an SVG, with each pollutant assigned a distinct color via `d3.scaleOrdinal` and `d3.schemeCategory10`. The code uses `d3.csv` to load the dataset, `d3.timeParse` to convert dates, and `d3.line` to generate the paths. Axes are rendered with `d3.axisBottom` and `d3.axisLeft`, and a legend is placed at each line’s final data point.