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. D. F., and Osses, M.: VEIN v0.2.2: an R package for bottom-up
  vehicular emissions inventories, Geosci. Model Dev., 11, 2209-2229,
  https://doi.org/10.5194/gmd-11-2209-2018, 2018.

A BibTeX entry for LaTeX users is

  @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://gmd.copernicus.org/articles/11/2209/2018/},
    doi = {10.5194/gmd-11-2209-2018},
  }

  Ibarra-Espinosa S (2024). _vein: Vehicular Emissions Inventories_. R
  package version 1.1.3, <https://CRAN.R-project.org/package=vein>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {vein: Vehicular Emissions Inventories},
    author = {Sergio Ibarra-Espinosa},
    year = {2024},
    note = {R package version 1.1.3},
    url = {https://CRAN.R-project.org/package=vein},
  }

Thanks