“…Previous reviews have shown that particulate matters (PMs), carbon monoxide (CO), carbon dioxide (CO 2 ), sulfur dioxide (SO 2 ), nitrogen dioxide (NO 2 ) and heavy metals were the major indoor air pollutants in the GCC countries (Abdul-Wahab and Al-Rehaili, 1999;Al Mulla et al, 2015;Argyropoulos et al, 2016;Elsayed et al, 2016;Farahat, 2016;Omidvarborna et al, 2018;Saraga et al, 2017). Recent studies in KSA have identified Radon ( 222 Rn) gas as another indoor air pollutant (Abo-Elmagd et al, 2018;Alghamdi and Aleissa, 2014). Moreover, it has been reported that indoor air pollution in most cities in the GCC region is due to the infiltration of ambient air pollutants into residential buildings, poor ventilations, burning of biomasses (Arabian incense), and overcrowding (Argyropoulos et al, 2016;Fadeyi et al, 2014;Jomehzadeh et al, 2017;Weitzman et al, 2016;Yaghi and Abdul-Wahab, 2003).…”