Abstract
From 2012 to 2015, we measured surface ozone, NOx, NO2, and NO levels at three urban sites (Mapipa, Ubungo, and Posta) and two suburban sites (Kunduchi and Vijibweni) in the city of Dar es Salaam and in the village of Mwetemo, a rural area of Bagamoyo, Tanzania. The average hourly O3 concentrations at all sites were between 9 ppb and 30 ppb during our sampling periods. O3 levels at suburban sites were generally higher than at urban sites. The average hourly concentrations in Dar es Salaam were 10 - 32 ppb, while in Bagamoyo they were 9 - 15 ppb. We observed a strong diurnal variation in Dar es Salaam while measurements from Bagamoyo showed little variation. At Dar es Salaam, the surface O3 concentrations increased from their minimum level at sunrise (around 6:00 a.m.) to a maximum in the late afternoon (around 4:00 p.m.), and then decreased toward 11:00 p.m. Another secondary ozone peak appeared between midnight and ~4:00 a.m., after which the surface ozone concentrations decreased to a minimum around 7:00 a.m. NO2 concentrations were higher at the urban sites of Ubungo and Posta, and their weekly average NO2 concentrations were 246 ppb and 118 ppb, respectively. Weekly average NOx concentrations ranged from 39.4 ppb at the Kunduchi site (suburban) to 738 ppb at the Ubungo site (urban). To our knowledge, there were few continuous measurements of ozone and nitrogen oxides concentrations in Tanzania. Since high NOx concentrations were observed, continuous air quality monitoring and effective air pollution control measures are required in Dar es Salaam to prevent further deterioration of air quality and limit the possible negative impacts on humans and vegetation.
Highlights
Elevated tropospheric ozone (O3) concentrations have received extensive attention around the world because of the damage caused to human health and ecosystems [1]-[6]
We present and discuss ozone and nitrogen oxide concentrations in the city of Dar es Salaam and the Bagamoyo Pwani region of Tanzania, east Africa
Ozone concentrations decrease from 5:00 pm until 11:00 p.m. which coincides with decreases in solar radiation
Summary
Elevated tropospheric ozone (O3) concentrations have received extensive attention around the world because of the damage caused to human health and ecosystems [1]-[6]. Ozone is a secondary pollutant formed through complex photochemical reactions involving NOx (NO2 + NO) and Volatile Organic Compounds (VOCs) under favorable meteorological conditions such as high solar radiation and high temperatures [7]-[9]. In African cities, urban air pollution is emerging as a key threat to health, the environment, and the quality of life of millions of Africans as the levels of urbanization, motorization, and economic activity increase [10]. Anthropogenic air pollution caused by vehicular emissions, industrialization, and biomass burning has decreased air quality [11]-[13]. Two of the main traffic and fossil fuel combustion-derived pollutants are nitrogen oxides (NOx) and VOCs, which are the primary precursors of ground level ozone
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