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Transport of pollutants from eastern Colorado into the Rocky Mountains via upslope winds

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October 8, 2013
Aaron Piña
Hosted by Scott Denning (advisor), Russ Schumacher, Jay Ham (Soil and Crop Sciences)

Abstract

The confluence of mountain meteorology and major pollution sources conspire to transport pollutants across the Front Range, especially nitrogen species (NH3, NH4+, orgN, NO3-, and HNO3) 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 accumulate in alpine terrestrial and aquatic ecosystems. The focus of this study was to examine the meteorological conditions in which atmospheric deposition of pollutants at three mountain sites was anomalously high due to convective transport. We analyzed 19 years (1994-2013) of precipitation and wet deposition data from three 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 N 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 slopes 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 deposition of nitrogen into the Rocky Mountains.