This is an hourly time series of PM2.5 concentration, temperature, and relative humidity measured by a MetOne BAM-1020 in Sarajevo, Bosnia and Herzegovina. This dataset is associated with the following publication: Hagler, G., T. Hanley, R. Vanderpool, B. Hassett-Sipple, M. Smith, J. Wilbur, T. Wilbur, T. Oliver, D. Shand, V. Vidacek, C. D'Angelo, and R. Allen. PM2.5 Temporal Trends and Instrument Performance Assessment Over 2018-2019 in Sarajevo, BiH Jan 2020. In Proceedings, UIPS Conference 2020, Sarajevo, NA, BOSNIA, 01/31/2021 - 01/31/2021. Association of Consulting Engineers Bosnia and Herzegovina, Sarajevo, BOSNIA, (2020).