This interactive visualization displays the average Air Quality Index (AQI) per month in Bangor, Maine, for years 2018 through 2022. A slider at the top lets users select a year, triggering a two-second animated transition of the bar chart. The code uses d3.v4 with a d3-queue to load multiple CSV files containing monthly data. Bars are drawn as SVG rectangles, with fill colors mapped through a d3.scaleQuantile. The y-axis scale remains fixed at 0 to 50, while each year’s data updates smoothly via `transition.attr` calls.