A detailed description of the methods used to develop this data are described in the following peer reviewed paper:
Hammer, M. S., A. van Donkelaar, C. Li, A. Lyapustin, A. M. Sayer, N. C. Hsu, R. C. Levy, M. J. Garay, O. V. Kalashnikova, R. A. Kahn, M. Brauer, J. S. Apte, D. K. Henze, L. Zhang, Q. Zhang, B. Ford, J. R. Pierce, and R. V. Martin. 2020. Global estimates and long-term trends of fine particulate matter concentrations (1998-2018). Environmental Science & Technology, 54(13), 7879-7890. https://doi.org/10.1021/acs.est.0c01764.