10.22376/ijpbs.2019.10.1.p1-12 Volume 1 Issue 2 2010 (April - June) Forty eight hour PM2.5 of trace metals measured concurrently revealed high indoor trace metals concentrations in PM2.5 when compared to the levels in ambient air (outdoor) irrespective of the four areas each, from the six Kuwait Governorates. Among the different indoor premises, Supermarkets showed high trace metals in PM2.5 followed by Retail shops greaterThan restaurants greaterThan Government offices greaterThan Private offices greaterThan storehouses attributing the inflow of outdoor dust particles and human activities. Governorate-IV showed high trace metals in PM2.5 collected from indoor premises than the other Governorates samples indicating the thickly populated and commercial importance of this Governorate. Metals wise analysis revealed high Aluminum (Al) concentrations irrespective of the different premises from the Governorate areas. In the present study, the high Indoor (I) /Outdoor (O) ratio ( greaterThan 1) in Fe, Al and Pb indicated the influence of indoor commercial activities and population spurt in Kuwaiti residents rather than the influence of outdoor dust accumulation. Although the sampled outdoor air has been traditionally considered rich in coarse PM particles, the present study suggest that indoor trace metals concentrations are dominated by the contribution of fine PM2.5 particles. Thus this study provides the characterization of outdoor and indoor aerosol concentrations in different areas and conditions that may lead to detrimental effects to residents in Kuwait. Ah Bu Olayan and B .V. Thomas Indoor pollution, I/O ratio, trace metals and Kuwait -