Determination of Selected Indoor and Outdoor Air Pollutants in the Central Business District of Nairobi City, Kenya

Abstract

The atmosphere is a complex environment that coexist gas species, solid particles and liquid droplets. When these substances are in amounts that could be harmful to the' health or comfort of humans and animals or which could cause damage to plants and materials, air pollution is said to occur. Some of the well known effects associated to air pollution include pulmonary and cardiovascular diseases, reduced visibility, acidification of soils and waters and accelerated decay of building materials and paints. Air pollution studies, for a long time concentrated on outdoor measurements, but recent findings show that indoor concentrations are greater than five times the corresponding outdoor levels and therefore making it ranked as one of the top five environmental hazards to human health considering that most urban people spend 90% of their time indoors. In Kenya, most air pollution measurements concentrated on outdoor environment with very little on indoor air pollution reported. The present study determined and compared indoor and outdoor levels of particulate matter (PM 10), heavy metals (Pb, Zn, Mn, Cu,) in PMlO and noxious gases (S02, NO, N02, and CO) in Nairobi central business district from March - November 2007. The PMlO were sampled using a Gent aerosol sampler and the heavy metals in the particulate matter determined by Xray fluorescence technique. Gases were collected and analysed using direct reading gas sensors. Statistical analysis of PMlO results show that 53% indoor measurements had higher concentration levels compared to corresponding outdoors (I/O ratio >1.0). The mean average concentrations were 377.0 ± 197.7!lg/M3 and 280.1 ± 122.5!lg/M3 for indoor and outdoor respectively. However, indoor/outdoor ratio analyses for heavy metals indicate higher concentrations in outdoors compared to corresponding indoors (I/O ratio=0.9). Noxious gases' ratios had indoor concentrations greater than outdoor suggesting indoor levels being influenced by indoor activities. Correlation analyses of PMlO, heavy metals and gases between regions indicate significant positive and negative relationships (P > 0.050) suggesting differences in activities in the regions. Most concentration levels of PMlO and heavy metals surpass the set maximum concentration limits while gases were within. It is hoped that the Ministry of Nairobi Metropolitan and interested stakeholders use this baseline data to come up with measures to mitigate emission of air pollutants in Nairobi city as envisioned in the Nairobi Metropolitan vision 2030 blueprint; "A World Class African Metropolis" .