@misc{indiciae804d6a874b0b,
  title = {External quality-assurance results for the National Atmospheric Deposition Program/National Trends Network during 1989},
  author = {T. C. Willoughby and J.D. Gordon and L.J. Schroeder and M.A. Nilles},
  year = {1991},
  doi = {10.3133/wri914039},
  url = {https://pubs.usgs.gov/publication/wri914039},
  note = {Source identifier: wri914039}
}