Spatial-Temporal Variability Of Tropospherical Ozone In City Of Nairobi, Kenya

ABSTRACT

Nairobi is an urban city whoseair pollution is increasingly being recognizedas a major

publichealthandenvironmentalissue.This is due to poor or deterioratingair quality

which is as aresultsof high levels of energy consumption by industries, transport

and domestic use. Thenatureofairpollutionisdependentonthesourceprofile of thecity

and the presence ofsunlight topromote production ofsecondary pollutants, such as

ozone, through photochemical reactions. The study sought to analyze the spatialtemporal

variability of surface ozone over the city of Nairobi, and identify the

source region. Surface ozone data for Nairobi was obtained from Kenya Meteorological

Department ranging from the year 2011 to 2014. Another set of data was collected

fromfour sampling sites for a period of ten days to determine the special variability and

source of the surface ozone over the city of Nairobi. . Analysis of meteorological field

from National Centre for Environmental Prediction -National Centre for Atmospheric

Research (NCEP- NCAR) was used in running Hybrid Single Particle Lagrangian

Integrated (HYSPLIT)model. From the analysis it was found out that June, July and

August experienced the highest ozone levels compared to the other months of the year in

both lower and upper levels. This was due to incursion from the south according to the

backward trajectories from the HYSPLIT model, which has been proven to have high

ozone concentration during this season due to high biomass burning. On the other hand,

the diurnal variation of ozone in the foursampling sites namely Industrial Area,Nakumatt

Junction, Landhies Road and Pangani Roundabout, showed low ozone levels in the early

morning and at night hours, with the peak realized during the day. The peak in midday

could be due to the fact that surface ozone was produced by photochemical oxidation of

precursor gases that are produced by motor vehicle and industries. The highest eight-hour

mean was 20.2 ppb from industrial area site, which is below the WHO mean of 51 ppb.

Therefore, no much health effects are expected due to the exposure to surface ozone. It is

recommended that there should be a continuous monitoring of surface ozone and other

gases that are harmful to human health for better understanding and advice to the citizen.