Abstract:
Nitrogen oxides (NOx) and carbon monoxide (CO) are the two important pollutants in the
atmosphere which are particularly emitted from vehicles. In this study, assessments were made
on hourly, daily, monthly and seasonal variability of the two gases along with their dependence
on two atmospheric variables (temperature and relative humidity) using one year data (2016) of
Addis Ababa. The data were obtained from Ethiopian Meteorological Agency, Addis Ababa. The
results of the analyses show the following. Hourly variability show peaks before noon (10:00 –
12:00) and around midnight. Variability of both pollutants among days did not show patterns.
But there seems to be correlation between NOx and CO concentrations on daily basis. Monthlyaveraged
concentrations showed seasonal patterns with variability between dry and wet seasons.
NOx concentration during wet season was about twice that of the dry season, but no such
difference was observed in the case of CO. Annual dependences of the two pollutants on the two
atmospheric variables, temperature and relative humidity, indicate modest negative correlation
between NOx and temperature but none for CO. Seasonally CO showed correlation with
temperature. NOx showed positive and CO negative, correlations with relative humidity on
seasonal basis. The data for NOx during the months September to December seem to have
problems and hence more year data may be needed to make reasonable conclusions.
