The comparison between in-situ monitored data and modelled results of nitrogen dioxide (NO2): case-study, road networks of Kigali city, Rwanda

Elisephane Irankunda; Zoltán Török; Alexandru Mereuță; Jimmy Gasore; Egide Kalisa; Beatha Akimpaye; Theobald Habineza; Olivier Shyaka; Gaston Munyampundu; Alexandru Ozunu

doi:10.1016/j.heliyon.2022.e12390

The comparison between in-situ monitored data and modelled results of nitrogen dioxide (NO₂): case-study, road networks of Kigali city, Rwanda

Heliyon. 2022 Dec 17;8(12):e12390. doi: 10.1016/j.heliyon.2022.e12390. eCollection 2022 Dec.

Affiliations

¹ Faculty of Environmental Science and Engineering, University of Babeş-Bolyai, 30 Fantanele Street, RO-400294 Cluj-Napoca, Romania.
² College of Science and Technology, University of Rwanda, KK737 Street, PO BOX 4285, Kigali, Rwanda.
³ Division of Environmental Compliance and Enforcement, The Rwanda Environment Management Authority, KG 7 Street, Kigali Rwanda, PO BOX 7436, Kigali, Rwanda.
⁴ Department of Technical Expert, Rwanda Space Agency, KG 7 Street, PO BOX 6205, Kigali, Rwanda.

Abstract

The incomplete combustion of fossil fuels from petrol, natural gas, and fuel oil in the engine of vehicles contributes to air quality degradation through traffic-related air pollutant emissions. The Real-time affordable multi-pollutant (RAMPs) monitors were installed in Kigali, the capital of Rwanda, to fill the gap in air quality datasets. Using RAMPs, this is the first air quality modelling research in Rwanda aiming to report the concentration of NO₂ by comparing In-situ monitored data and modelled results. We targeted NO₂ emissions from 27 road networks of Kigali to address the impacts of traffic emissions on air quality over 2021. The American Meteorological Society and Environmental Protection Agency regulatory models (AERMOD and ISCST3) were used for simulation. Statistical indexes include fractional bias (FB), the fraction of the prediction within the factor of two of the observations (FAC2), normalized mean square error (NMSE), geometric mean bias (MG), and geometric variance (VG) used to assess models' reliability. Monitoring shows the annual mean of 16.07 μg/m³, 20.35 μg/m³, and 15.46 μg/m³ at Mont-Kigali, Gacuriro, and Gikondo-Mburabuturo stations, respectively. Modelling shows the daily mean of 111.77 μg/m³ and annually mean of 50.42 μg/m³ with AERMOD and daily mean of 200.26 μg/m³ and annually mean of 72.26 μg/m³ with ISCST3. The FB, NMSE, and FAC2 showed good agreement, while MG and VG showed moderate agreement with AERMOD. The FB, NMSE, and MG showed moderate agreement, while FAC2 and VG disagreed with ISCST3. Traffic and urban residential emissions were identified as potential sources of NO₂. Results indicated that Kigali residents are exposed to a significant level of NO₂ exceeding World Health Organisation limits. Findings will help track the effectiveness of Rwanda's recently executed pollution-control policy, suggest evidence based on the recommendations to reduce NO₂, and use further dispersion models to support ground-based observations to improve public health.

Keywords: AERMOD; ISCST3; In-situ monitoring; Kigali city; NO2; Traffic emissions.