The indoor air quality of four Local Government Areas of Lagos State, Nigeria (Eti-Osa, Ikeja, Surulere, and Apapa) were monitored in this study. Six sample locations in each of the selected Local Government Areas were assessed for Particulate Matter (PM2.5 and PM10), Temperature, Relative Humidity, Hydrogen Sulphide (H2S), Noise level, Carbon Monoxide (CO), Volatile Organic Compounds (VOCs), Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2), and Ammonia (NH3); by using handheld testers which were verified before use for quality assurance. Results across the four Local Government Areas show that the levels of PM2.5 (4-37µg/m3), PM10 (7-77 µg/m3), relative humidity (63-99%), noise level (41.8-81.8dBA), CO (001-138ppm), VOCs (-2 to 12ppm), SO2 (0.0-0.6ppm) exceeded the regulatory limits of various organizations including WHO, NAAQS, OSHA. Furthermore, results obtained show that two sample points in Ikeja Local Government Area had CO value that is significantly higher than the regulatory limits (P<0.001,0.01,0.05) with values of 138 and 122ppm as against the permissible standard of 11ppm on an 8-hour exposure. Eti-Osa also had a very significant concentration of PM2.5 (37µg/m3) and SO2 (0.6ppm) in two of its sampling points respectively which exceeded the acceptable NAAQS limits of 15 µg/m3 and 0.38ppm respectively. It is evident from the results obtained in the study that there are dangers posed by poor indoor air we are exposed to on daily basis and as such, public awareness is pertinent; because we spend more time indoor than outdoor. The evidence therefore suggests that; with the introduction of the monitoring of indoor ambient air parameters, would be an accompanied reduction in air pollution related health conditions.
Key Words: Pollutants, Indoor air quality, Concentration, Sampling point, Local Government Areas