To cite vein in publications use at least the first, if not both, thanks:

Ibarra-Espinosa, S., Ynoue, R., O'Sullivan, S., Pebesma, E., Andrade, M. D. F., and Osses, M. (2017). VEIN v0.2.2: an R package for bottom-up Vehicular Emissions Inventories Geosci. Model Dev. Discus, https://doi.org/10.5194/gmd-2017-193, in review, 2017.

Sergio Ibarra-Espinosa (2017) vein: Vehicular Emissions Inventories. R package version 0.2.2-25. https://CRAN.R-project.org/package=vein

Corresponding BibTeX entries:

  @Article{,
    title = {VEIN v0.2.2: an R package for bottom-up Vehicular
      Emissions Inventories},
    journal = {Geoscientific Model Development Discussions},
    author = {Sergio Ibarra-Espinosa and Rita Ynoue and Shane {O'
      Sullivan} and Edzer Pebesma and Maria de Fatima Andrade and
      Mauricio Osses},
    year = {2017},
    url = {https://www.geosci-model-dev-discuss.net/gmd-2017-193},
  }
  @Manual{,
    title = {vein: Vehicular Emissions Inventories},
    author = {Sergio Ibarra-Espinosa},
    year = {2017},
    note = {R package version 0.3.9},
    url = {https://CRAN.R-project.org/package=vein},
  }