Air Quality Alerts, Health Impacts, and Adaptation Implications Under Varying Climate Policy

Without emission reductions, climate change may increase ozone and PM_2.5 air pollution in the United States; however, we do not know how this will affect air quality alerts that prompt people to stay indoors. Here, we use an integrated modeling framework to find distributions of daily Air Quality Index (AQI) during the smog season at the start, middle, and end-of-century. Considering natural variability, climate change may cause air quality alerts to double (increase by a factor of 2 ± 0.2) by 2100. Days when both ozone and PM_2.5 exceed alert thresholds quadruple (4.3 ± 1.2). More than 100,000,000 (±45,000,000) people experience mean air pollution deemed "Unhealthy for Sensitive Groups", a growth of 7 (±3) times compared to 2000. If people follow alerts by staying inside, they reduce exposure to outdoor-generated pollutants. Their health benefits are similar whether the alert is caused by ozone or PM_2.5. Senior (age 65+) populations receive much higher benefits per day by adapting (e.g., 95CI for PM_2.5: $4.60 to $147) as young adults (age 18-35; 95CI: $0.15 to $4.22)─more than 45 times higher on average. This disproportionate impact requires targeted messaging and guidance, especially as climate-related risks rise.