Exposure to black carbon—fine soot particles from combustion sources—over just 28 days significantly increased depression and anxiety scores in 2,271 middle-aged and older Chinese adults. The pollution elevated depression risk by 55% and anxiety risk by 63%, with measurable impacts on standardized mental health questionnaires. Researchers identified 113 specific DNA methylation sites in mitochondrial regulatory genes that changed with black carbon exposure. Three particular sites in genes SLC25A38, SLC25A37, and SLC25A35 mediated up to 25% of pollution's depression effects. This finding represents a breakthrough in understanding how air pollution damages mental health at the molecular level. Previous research established links between long-term air pollution and cognitive decline, but this study reveals rapid epigenetic changes affecting cellular energy production within weeks. The mitochondrial connection is particularly significant because these organelles power brain function and are vulnerable to oxidative stress from pollutants. Interestingly, good sleep quality appeared protective against these effects, suggesting behavioral interventions might buffer environmental damage. For urban populations facing unavoidable pollution exposure, this research highlights both the urgency of air quality improvements and the potential for targeted interventions protecting mitochondrial function and sleep hygiene as mental health strategies.