Waterloo Modeling Predicts Sevenfold Increase in Unhealthy Air Alerts by 2100, Affecting 100 Million Americans

University of Waterloo study finds 100 million Americans will face routine unhealthy air by 2100, with California and the East Coast at highest risk.

By: AXL Media

Published: Mar 31, 2026, 6:15 AM EDT

Source: Information for this report was sourced from University of Waterloo.

The Shift from Rare to Commonplace Pollution

For decades, air quality alerts have been viewed as occasional disruptions caused by specific weather patterns or nearby wildfires. However, new international modeling suggests a fundamental shift in the American atmosphere. By 2100, almost 30% of the U.S. population will routinely breathe air deemed "unhealthy for sensitive groups." This sevenfold increase is driven by the intensifying interplay between rising global temperatures and the formation of ground-level ozone and particulate matter—the two primary components of smog.

Mapping the "Smog Season" Surge

The research team, led by Dr. Rebecca Saari, identified California and the Eastern United States as the primary hotspots for this atmospheric decline. During the peak smog season, which spans from May 1 to September 30, the number of people living in poor air quality zones is projected to jump from 14 million (at the turn of the century) to 100 million. This change would require vulnerable individuals—including the elderly and children with asthma—to stay indoors for an additional 142 days per year to avoid significant health risks.

Vulnerable Populations and the "Coin Flip" Reality

Dr. Saari, the Canada Research Chair in Global Change, Atmosphere and Health, describes the future for sensitive groups as a "daily coin flip." In many regions, the odds of receiving a government alert advising residents to change their behavior will be nearly 50/50. For seniors and those with chronic respiratory or cardiovascular conditions, this persistent exposure is a primary contributor to premature death and long-term sickness.