(52a) Modeling the Source Sectors Contribution to Nitrogen Deposition in U.S. Hydrological Regions

The excessive deposition of atmospheric nitrogen containing species to aquatic systems and watersheds can lead to harmful algae growth and loss of biodiversity, particularly in coastal waterways. It increases the risk of acidification and hypoxia by reducing oxygen levels for living organisms in marine environments. It is important to determine the major species, source sectors, and source regions responsible for atmospheric nitrogen deposition to develop effective watershed management systems. We use the Comprehensive Air Quality Model with extensions (CAMx) version 6.0, along with the Particulate Matter Source Apportionment Technology (PSAT), to identify and separate source sector contributions to atmospheric nitrogen deposition. We model the amount of atmospheric nitrogen deposition from electricity generating units, biogenic emissions, area fugitive dust, on-road, residential wood combustion, agricultural emissions, non-point source oil and gas, point source oil and gas, fires, non-road mobile equipment sources, marine vessels and locomotives, and other non-point sources in the contiguous United States, southern Canada, and northern Mexico. We use emissions, meteorology, boundary conditions, and ozone column inputs from the United States Environmental Protection Agency’s 2011 Modeling Platform. We evaluate the wet and dry deposited mass of atmospheric nitrogen containing species against measurements. This information will aid environmental regulators in developing watershed management plans to protect the health of aquatic and terrestrial ecosystems. The Upper Mississippi hydrologic region experienced the highest flux of gaseous ammonia deposition, and the dominant source sector was agricultural ammonia emissions. The Ohio region received the highest flux of reactive gaseous nitrogen , mostly from on-road emissions. Reactive gaseous nitrogen deposition from biogenic and electricity generating source sectors were significant throughout the United States.