This study examines associations between acute changes in ambient PM2.5 and circulating levels of ET-1. It also looks at whether changes in ET-1 are associated with changes in markers of vascular health and systemic injury. Findings of the study further reveal the insidious nature of PI2.5’s anti-angiogenic effect, including a novel relationship between ET-1 and CACs in young adults exposed to acute elevations of air pollution.