Convective transport of pollutants from eastern Colorado concentrated animal feeding operations into the Rocky Mountains

As the population of the urban corridor along the eastern Front Range grows at an unprecedented rate, concern about pollutant transport into the Rocky Mountains is on the rise. The confluence of mountain meteorology and major pollution sources conspire to transport pollutants across the Front Range, especially nitrogen species (NH₃, NH₄⁺, orgN, and NO₃^-) from concentrated animal feeding operations and urban regions, into the Rocky Mountains. The Rocky Mountains have coarse-textured soils which disallow the uptake nitrogen-rich precipitation, allowing most ions in precipitation to reach, be stored in, and eutrophicate alpine terrestrial and aquatic ecosystems. The focus of this study was to examine the meteorological conditions in which atmospheric deposition of pollutants at two mountain sites was anomalously high due to convective transport. We looked at 19 years (1994-2013) of precipitation and wet deposition data from two National Atmospheric Deposition Program (NAPD) sites in the Rocky Mountains: Beaver Meadows (CO19) and Loch Vale (CO98). Loch Vale (3159 m) and Beaver Meadows (2477 m) are located approximately 11 km apart but differ in height by 682 m resulting in different seasonal precipitation composition and totals. The Advanced Research WRF model was used to simulate the meteorology at a high resolution for the progression of the upslope event that led to high nitrogen deposition in the Rocky Mountains. Data from the North American Regional Reanalysis (NARR) was used to observe and verify synoptic conditions produced by the WRF model that influenced the high-deposition events. Dispersion plumes showed a mesoscale mountain circulation caused by differential heating between mountains-tops and the plains was the main driver of the westward convective transport towards the mountains. Additionally and unexpectedly, a lee trough and high precipitable water values associated with a cold front played significant roles in the nitrogen deposition into the Rocky Mountains.