Enhancing wet-deposition maps with urban data: Preliminary results from the Network for Urban Atmospheric Nitrogen Chemistry
Gregory Wetherbee1, Jack McDonnell2, Dillon McClintock-Rager3, Amy Ludtke4, RoseAnn Martin5, Brian Kerschner6, Lisa Devore7, Jill Webster8, Jon Novick9, Sheila Murphy10 and A. Scott Kittelman11
For forty years, the National Atmospheric Deposition Program (NADP) has emphasized monitoring at sites where the chemical composition of precipitation is expected to be regionally representative and not influenced by specific emission sources, which are ubiquitous in urban areas. Data from NADP sites designated as urban-influenced are omitted from inclusion in the spatial interpolation processes used to prepare some NADP mapping products to prevent excessive urban influence on surrounding areas. However, the converse is also true, whereby data from regionally representative sites is not representative of urban wet deposition. One of the objectives of the Network for Urban Atmospheric Nitrogen Chemistry (NUANC) is to evaluate the appropriate radius of influence of urban wet-deposition data for NADP’s interpolated maps and other products.
The NUANC consists of 5 NADP National Trends Network (NTN) sites specifically installed to collect urban wet-deposition data across the Denver, CO metropolitan area. These 5 sites are aligned in a southeast to northwest transect. In addition, three more NTN sites are included to extend the transect. These 3 sites are in the foothills and mountains of the Front Range, terminating with the Loch Vale site in Rocky Mountain National Park. Weekly samples were analyzed for a suite of constituents, including nitrate and ammonium concentrations, which are used to calculate weekly and annual precipitation-weighted inorganic reactive nitrogen (Nr) concentrations and deposition for each site. The NUANC annual deposition results were included with data from regionally representative sites to create interpolated wet-deposition maps.
Maps with and without the NUANC data were compared. Inclusion of the NUANC data in the wet-deposition maps resulted in a 50 percent increase in estimated Nr wet deposition in the Denver – Boulder urban corridor compared to maps that used only regionally representative data. Not only is the spatial representation of Nr wet-deposition improved, but the NUANC data also allows for more representative estimation of the potential Nr loading to the South Platte River watershed. Assuming an annual runoff coefficient of 0.1, at least 10 percent of the Nr load in the South Platte River was from atmospheric deposition during 2017.
1U.S. Geological Survey, wetherbe@usgs.gov
2Colorado Department of Public Health and Environment Air Quality Control Division, jack.mcdonnell@state.co.us
3Colorado University, Dillon.Ragar@colorado.edu
4USGS-retired, asludtke@gmail.com
5U.S. Geological Survey, ramartin@usgs.gov
6University of Illinois, bmkersch@illinois.edu
7Colorado Department of Public Health and Environment Air Quality Control Division, lisa.devore@state.co.us
8U.S. Forest Service, Jill_Webster@usfws.gov
9City and County of Denver, Jon.Novick@denvergov.org
10U.S. Geological Survey, sfmurphy@usgs.gov
11Colorado University, alan.kittelman@colorado.edu