Four time-series scatter plots visualize daily measurements of airborne particulate concentration, pressure, air temperature, and wind speed from 2018. The plots use D3 version 5's `scaleTime` for the date axis and `scaleLinear` for the value axis, rendering each day as a circle via SVG. Brushing is implemented with `brushSelection` from D3, which highlights brushed circles in magenta and dims the rest to gray.