Using two decades of U.S. county-level data, researchers found that long-term PM2.5 exposure was robustly associated with higher childhood ADHD prevalence, while associations with low birth weight and diabetes weakened after accounting for county-specific temporal trends. The ADHD association persisted after socioeconomic, demographic, state-level, exposure-period, and spatial adjustments, although the ecological study cannot establish an individual-level causal relationship.