Nitrogen transport and deposition during the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study

A number of deleterious effects have been noted due to increasing deposition of nitrogen compounds in Rocky Mountain National Park (RMNP). The Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study was conducted to improve our understanding of the sources and transport of airborne nitrogen and sulfur species within RMNP as well as their deposition pathways. Two field campaigns were conducted, in spring and summer 2006, to characterize pollutant transport and deposition during seasons with historically high nitrogen inputs. Several measurements sites were operated within the park, at locations west and east of the park boundaries, and at locations near the NE, NW, and SE boundaries of the state of Colorado. Measurements at several sites included 24-hour integrated gas concentrations (ammonia, nitric acid, sulfur dioxide), PM2.5 composition, and wet deposition. A core measurement site in the park included more detailed and higher time resolution chemical, optical, and particle size distribution measurements. An overview of study findings will be presented including the composition of collected PM2.5, concentrations of key trace gas species, and observations of wet and dry deposition composition and fluxes. Concentrations of N species in RMNP varied significantly with local and regional transport patterns. High concentrations of nitrate/nitric acid and ammonia/ammonium observed routinely on the eastern plains of Colorado reflect a mixture of urban and agricultural emissions. The highest concentrations of N species in RMNP were generally associated with upslope transport from the east. Nitrogen deposition in RMNP during the spring campaign was dominated by a single, upslope snowstorm. A combination of high pollutant concentrations and heavy precipitation during this upslope event acted to produce N deposition fluxes that far outweighed other spring precipitation events. During the summer study, by contrast, numerous events contributed more equally to total N wet deposition fluxes. Organic nitrogen, ammonium, and nitrate were all important contributors to N wet deposition. Wet deposition of N substantially exceeded dry deposition inputs.