Magnitude and variation of traffic air pollution as measured by CO in the City of Addis Ababa, Ethiopia

Background: Air pollution level in Addis Ababa is presumed to be high due to the prevalence of old vehicles and substandard road infrastructures. This study assessed CO concentration as a measure of traffic air pollution. Materials and methods: a total of 80 road side and 24 on-road daily traffic air samples during wet and dry seasons of 2007 and 2008, respectively, were taken using CO data logger. A structured checklist was used to document related data. Downloaded data from the CO sampler was used to generate summary statistics and data presentations. Data quality of CO measurement was ensured using calibration checks. Results: The mean for 15 minutes CO concentration was 2.1 ppm (GM=1.3) and 2.8 ppm (GM=2.2) for wet and dry seasons, respectively. The concentrations from season to season varied statistically. The CO temporal and spatial profiles among the two seasons were similar. The overall mean on-road CO concentration was 5.4 ppm (GM=5.3). Fifteen percent of roadside samples and all on-road samples exhibited more than 50% of the 8-hr CO WHO guideline.. Daily CO maxima were observed in early mornings and late afternoons. Conclusions: The consistency in spatial and temporal profiles and the variation on both on-road and road side traffic lines imply that vehicles are the main source of traffic air pollution. There is a concern that the CO 8-hr World Health Organization guideline might be exceeded in future.