On ground truth in cross-border ozone transport.

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Air Pollution Management

Background:

• Cross-border ozone transport is a significant challenge in U.S. air pollution management.
• Current air quality models lack sufficient validation due to a scarcity of observational studies on ozone transport itself.

Purpose of the Study:

• To demonstrate a method for extracting observation-based benchmarks of cross-border ozone transport from rural monitoring data.
• To address the inadequacy of using ozone concentration validation alone for cross-border transport models.

Main Methods:

• Developing a technique to derive cross-border ozone transport benchmarks from rural monitoring sites near state borders.
• Analyzing ozone data from western New York's border to assess the origin of high pollution days.

Main Results:

• In two-thirds of high pollution days, ozone at the western New York border originated from cross-border inflow after passing over urban areas.
• On these days, ozone concentrations upwind of the border averaged 68 ppb, nearing the 70 ppb regulatory threshold.

Conclusions:

• Model validation for cross-border ozone transport requires benchmarks of transport, not just concentrations.
• Rural monitoring sites near state borders are valuable for generating these essential observation-based benchmarks.