Of the Door County generated emissions, 53 percent of NOx (Nitrogen Oxide) emissions came from commercial marine vessels on Lake Michigan, and 61 percent of VOC (Volatile organic compounds) emissions came from recreational vehicles and pleasure craft.

The monitor at Newport State park is near the shore. When ozone-rich air from over the lake flowed downwind to onshore locations, air with the highest ozone concentrations mixed down to the surface first, causing the highest ozone observations along the shoreline. Eventually air from higher altitudes mixed down to the surface farther inland, diluting the overall ozone mixing ratios for areas further inland.

The monitor has been in place since 1989.