Data for "Ammonia Dry Deposition in an Alpine Ecosystem Traced to Agricultural Emission Hotpots"

Elevated reactive nitrogen (Nr) deposition is a concern for alpine
ecosystems, and dry NH3 deposition is a key contributor. Understanding how
emission hotspots impact downwind ecosystems through dry NH3 deposition
provides opportunities for effective mitigation. However, direct NH3 flux
measurements with sufficient temporal resolution to quantify such events
are rare. Here, we measured NH3 fluxes at Rocky Mountain National Park
(RMNP) during two summers and analyzed transport events from upwind
agricultural and urban sources in northeastern Colorado. We deployed
open-path NH3 sensors on a mobile laboratory and an eddy covariance tower
to measure NH3 concentrations and fluxes. Our spatial sampling illustrated
an upslope event that transported NH3 emissions from the hotspot to RMNP.
Observed NH3 deposition was significantly higher when backtrajectories
passed through only the agricultural region (7.9 ng m-2 s-1) versus only
the urban area (1.0 ng m-2 s-1) and both urban and agricultural areas (2.7
ng m-2 s-1). Cumulative NH3 fluxes were calculated using observed,
bidirectional modeled, and gap-filled fluxes. More than 40% of the total
dry NH3 deposition occurred when air masses were traced back to
agricultural source regions. More generally, we identified that 10 (25)
more national parks in the U.S. are within 100 (200) km of an NH3 hotspot,
and more observations are needed to quantify the impacts of these hotspots
on dry NH3 depositions in these regions. Download the README.txt file for
a detailed description of this dataset's content.