Historically, air quality in the San Juan Mountains has been among the cleanest in the United States. However, concerns about mercury, ground-level ozone, nitrogen, and other pollutants are growing. Mercury concentrations in precipitation are alarmingly high and several water bodies have mercury ﬁsh consumption advisories. Ozone is approaching the limit for public health, and nitrogen levels in rain and snow are increasing. MSI ﬁlls data gaps by monitoring air pollution and its effects on environmental and human health. The Institute’s air quality outreach provides accurate, unbiased information to stakeholders and brings agencies, organizations, and individuals together in information-sharing and problem-solving forums.