A horizontal bar chart visualizes the volume percentage of gases composing dry air at sea level, with bar color shifting from deeppink to dodgerblue on hover and tooltips displaying the percentage in volume percent and ppmv. Built with D3.js v3, the chart uses `d3.scale.ordinal` and `d3.scale.linear` for axes, `d3.svg.axis` for tick marks, and the custom `d3.tip` library for interactive tooltips. Data is loaded from a CSV file containing atmospheric gas concentrations, and the visualization includes a rotating x-axis label for narrow screens.