Air Boundaries: Atmospheric Deposition Trends in North America

Conferencia de Cristopher Lehman

22 de Agosto del 2017 de 12:00 hrs

Air pollution knows no borders, and there is a need to better understand the long-range transport of atmospheric pollutants in North America and their spatial and temporal trends. The emission of air pollutants has direct and indirect impacts on human health and natural ecosystems. Air pollutants are removed from the atmosphere by two mechanisms: By dry deposition removal of particles and gases, and wet deposition removal in rain and snow. Environmental regulations in the United States (principally the Clean Air Act Amendments of 1990) have reduced the emission of air pollutants, which has mitigated the worst impacts of acid rain. However, there are continued concerns due to the deposition of nitrogen and mercury. These chemical species have a negative impact on water quality and threaten the aquatic food chain. Atmospheric deposition measurements represent some of the longest-term environmental monitoring data in North America. Since 1978, the National Atmospheric Deposition Program (NADP) has measured spatial and temporal trends in wet deposition. Its largest and longest-running network, the National Trends Network, currently measures spatial and temporal trends in acidic species, base cations, and nutrients at 269 stations in the United States, Canada and Argentina. There is interest in adding additional NTN sites in Mexico. NTN data are incorporated into the National Atmospheric Chemistry (NAtChem) Database, coordinated by Environment and Climate Change Canada, to characterize acidic deposition across North America. The NADP’s Mercury Deposition Network (MDN), founded in 1995, measures elemental and methyl mercury wet deposition at 108 sites in the US and Canada. Two stations operated in Mexico 2004 and 2005: Huejutla in the State of Hidalgo, and Puerto Angel in the State of Oaxaca. The NADP Atmospheric Mercury Monitoring Network (AMNet, founded in 2006) measures ambient elemental, ionic, and particulate mercury species at 23 US and Canadian locations.Two additional NADP networks characterize nitrogen and nutrient deposition: The Atmospheric Integrated Research Monitoring Network (AIRMoN, founded in 1992) collects event-based wet deposition samples at six sites. The Ammonia Monitoring Network (AMoN, founded in 2007) measures ambient atmospheric ammonia concentrations at 99 sites across the US and Canada. This presentation provides an overview of the NADP’s five atmospheric monitoring networks and evaluates long-term trends in atmospheric deposition. Urban areas are of particular concern, as atmospheric deposition in population centers represents the quality of air people breathe and the regional impacts of urban pollutants. Canada, Mexico, and the United States affect the common atmosphere of North America and it is important that we seek to achieve an understanding of the impacts of human activities on our shared air quality resource.