This visualization presents a scatter plot of London air quality measurements, comparing roadside versus background monitoring stations across time. Users can select different pollutants via a dropdown menu, while color encodes month and stroke distinguishes station type. The visualization includes interactive legends that filter data points by month or station type, with animated transitions updating circle positions. The code utilizes D3 v5 modules including `scaleTime`, `scaleLinear`, `scaleOrdinal`, `axisBottom`, `axisLeft`, and `interpolateBuPu` for color encoding, with data loaded from a CSV file using `d3.csv`.