The temporal cycles of carbon monoxide and Ozone and their impact on air quality over Nairobi

Abstract

This paper seeks to describe the determination of urban air quality of a certain area through monitoring of CO and O3. The diurnal variation of meteorological variables (temperature and wind), their interaction and effects on the diurnal cycles of carbon monoxide and ozone over is discussed. Hourly data for CO and O3 (surface ozone) the month of December (2011) and daily wind and temperature for the same period from Chiromo Environmental Monitoring station was used in this study. Time series analysis was used in this study to obtain the diurnal cycles of pollutants and the meteorological variables. Graphical method was useful particular in the physical representation of diurnal variation of the variables throughout the entire study period. The relationship between ozone and carbon dioxide and their interaction with wind temperature was determined with the use of correlation analysis method. Minimum ozone concentrations are observed between 0630h and 0730h and between 2030h and 2130h when highest CO concentrations are observed. During the early daylight and evening hours, pollutant concentration rises mainly due to the increase in traffic and acts as catalyst in the breakdown of O3. At midday (between1300h and 1400h) maximum ozone concentrations are observed whereas CO depicts low-level concentrations. During this period the atmosphere experienced a lot of conversion due to the thermal heating. Changes in day-to-day weather, is seen as a factor affecting the diurnal variation of CO and O3 as weather determines how quickly pollutants are dispersed away from an area. Weather also determines the thickness of the atmospheric layer, where the emissions are diluted in a vertical direction. The average concentrations of ozone were found to be 18.0+8.0ppb.Although O3 concentrations levels within the city of Nairobi are below the threshold levels set by WMO of 51ppb, the health impacts can be aggravated during midday compared to early mornings and evenings.