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

Ibarra-Espinosa S, Ynoue R, O'Sullivan S, Pebesma E, Andrade M, Osses M (2018). “VEIN v0.2.2: an R package for bottom-up Vehicular Emissions Inventories.” Geoscientific Model Development. doi: 10.5194/gmd-11-2209-2018, https://www.geosci-model-dev.net/11/2209/2018/.

Ibarra-Espinosa S (2019). vein: Vehicular Emissions Inventories. R package version 0.8.0, https://CRAN.R-project.org/package=vein.

Thanks

Corresponding BibTeX entries:

  @Article{,
    title = {VEIN v0.2.2: an R package for bottom-up Vehicular
      Emissions Inventories},
    journal = {Geoscientific Model Development},
    author = {Sergio Ibarra-Espinosa and Rita Ynoue and Shane
      O'Sullivan and Edzer Pebesma and Maria de Fatima Andrade and
      Mauricio Osses},
    year = {2018},
    url = {https://www.geosci-model-dev.net/11/2209/2018/},
    doi = {10.5194/gmd-11-2209-2018},
  }
  @Manual{,
    title = {vein: Vehicular Emissions Inventories},
    author = {Sergio Ibarra-Espinosa},
    year = {2019},
    note = {R package version 0.8.0},
    url = {https://CRAN.R-project.org/package=vein},
  }