This animated bubble chart visualizes real-time Air Quality Index (AQI) data for five major world cities, sourced from IQAir’s dynamic ranking. Circles radiate outward with staggered transitions, sized proportionally to each city’s AQI, with labels displaying city name and index value. Colored fills distinguish pollution levels, from hazardous Kinshasa in dark red to cleaner Yangon in white. Built with D3.js (v7), the visualization uses `transition` delays and easing to animate enter and update states, while hardcoded coordinates position cities horizontally. The code prepares for future features like city lookup by name or AQI, image annotations, and pairwise comparisons.