This scatter plot visualizes Air Quality Index (AQI) values over time, colored by the dominant pollutant type for each recorded date. Each circle represents a daily measurement, with the y-axis showing the AQI value and the x-axis encoding the date. The visualization is built using Vega-Lite’s API via `vega-lite-api`, with data loaded from a CSV file using `d3.csv`. A firebrick rule line marks a fixed y-value of 20, and tooltips display the specific pollutant and AQI value for each point.