This interactive scatter plot displays the relationship between particulate matter (PM2.5) levels in 2010 and 2018 across U.S. counties, with each circle representing a county. Built with a reusable D3.js component within a React application, it renders as an SVG using the `scaleLinear` API for axis scaling and `axisLeft`/`axisBottom` for chart annotations. The visualization leverages D3's `select` and `join` methods for efficient DOM manipulation, making it adaptable to different datasets through configurable accessor functions. Data is sourced from a CSV file containing historical PM2.5 measurements.