Norden, Norhanani Aina, et al. “A Study of Outdoor Concentrations of Particulate Matter (PM2.5) on Different Floors of a University Building”. Journal of Advancement in Environmental Solution and Resource Recovery, vol. 2, no. 2, Dec. 2022, pp. 12-18, https://penerbit.uthm.edu.my/ojs/index.php/jaesrr/article/view/12768.