Analysis of Ground Level Ozone and Nitrogen Oxides in the City of Dar es Salaam and the Rural Area of Bagamoyo, Tanzania

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.

Evaluation of low-cost electro-chemical sensors for environmental monitoring of ozone, nitrogen dioxide, and carbon monoxide

“…utilizes a semi-conductor oxide O 3 sensor (OZU 0–0.15 ppm), and has been used commonly for O 3 detection in air quality monitoring networks. [26–28] The operating principle of the Aeroqual S500 includes drawing sample air into an enclosure wherein the oxidizing capacity of the ozone molecules modifies the electrical state of a heated thin film of tungsten oxide as the sensing material. [26] Since the electrical conductivity of the material is a strong function of the temperature and RH, devices operating based on this semi-conduction oxidizing mechanism are not a reference method for the detection of O 3 .…”

Measurement report: Long-term measurements of ozone concentrations in semi-natural African ecosystems

“…Indeed, radiation and humidity facilitate the propagation of radical chain reactions and the production of hydroxyl radicals (OH) at these sites (Graedel and Crutzen, 1993). According to several authors, O3 levels tend to increase under warm, sunny conditions favorable to photochemical O3 production (Hamdun and Arakaki, 2015;Morakinyo et al, 2020). Moreover, Aghedo et al (2007), Mari et al (2011), Saunois et al (2009) and Saxton et al (2007) have reported that vegetated areas emit large quantities of biogenic organic compounds that influence O3 production in the presence of light and temperature.…”

“…Laban et al (2018) reported O3 levels in northeastern South Africa, and characterized the links between observed NOx and O3 concentrations. Other works were carried out by Bencherif et al (2020), Gaudel et al (2020), Hamdun and Arakaki (2015), Ihedike et al (2023), Josipovic et al (2010, Khoder (2009), Lee et al (2021), Ngoasheng et al (2021), Zunckel et al (2004) in different locations in Africa to characterize O3 pollution levels. Other projects such as POLCA (POLlution des Capitales Africaines) and DACCIWA (Interactions Dynamique-Aérosols-Chimie-Nuages en Afrique de l'Ouest), have also been implemented in African capitals such as Bamako, Dakar and Yaoundé (Adon et al, 2016), Abidjan, Cotonou (Bahino et al, 2018) and have provided O3 concentration surface measurements.…”

Tanzania Craton, Serengeti Plain and Eastern Rift Valley: mapping of geospatial data by scripting techniques

“…The environmental setting of Tanzania (see Fig. 1 for topography) has been continuously studied since the 1960s (James 1967;Kent et al 1971;Kajato 1982;Maboko and Basu 1987;Ijumulana et al 1997;Kabete et al 2012aKabete et al , 2012bBoniface 2014;Hamdun and Arakaki 2015;Gombe et al 2017;John 2020). Such attention can be explained by its unique environment, specific geologic setting and rich mineral resources.…”