Polycyclic aromatic hydrocarbons in urban air: Concentration levels, patterns, and source analysis in Nairobi, Kenya

This study describes polycyclic aromatic hydrocarbon (PAH) concentrations, patterns, and possible sources from atmospheric filter samples collected from three different areas in the city of Nairobi, Kenya. Total median concentrations for the 25 PAHs detected were higher in the traffic area ( 201 ng/m(-3)), followed by the residential area ( 141 ng/m(-3)), and lowest in the industrial area (128 ng/m(-3)). Results from the three sampled areas show that the percentage contributions of carcinogenic PAHs were approximately 30% of the total PAH concentrations reported. Some PAH isomer ratios differentiated traffic sources from non-traffic sources. Principal component analysis showed four significant principal components accounting for 82% of the variance. The first principal component (35%) was associated with fuel burning. The second principal component (27%) was associated with traffic emissions ( diesel and gasoline). The other two principal components, which accounted for 12% and 8%, could not be interpreted with certainty. In order to interpret all the principal components in relation to sources, further collection of data is needed. More data points would have helped in further resolving the sources because data analysis models recommend more than 30 data sets.