Evaluation of Pollutants Along the National Road N2 in Togo using the AERMOD Dispersion Model.

Background: Air pollution has become a major problem around the world and is increasingly an issue in Togo due to increased vehicular traffic. Gaseous pollutants are released by engines and are very harmful to human health and the environment. The fuels used on the major road in Togo, the N2, are adulterated with unknown contents and are of poor quality. Many of the vehicles come from neighboring countries, such as Benin, Ghana and Nigeria.

Objectives: The present study aims to evaluate the pollution rate in Togo through the estimation of the concentrations of sulfur dioxide (SO₂), nitrogen oxides (NO_x), and particular matter (PM) on the international road, the National Road N2, in Lomé, compared to the World Health Organization's (WHO) standard limit.

Methods: The simulations of pollutant concentration were performed using the Industrial Source Complex Short Term Version 3 model, which is included in the United States Environmental Protection Agency Regulatory Model (USEPA) AERMOD View software. The meteorological averages data were obtained from the local station near the National Road N2 in Togo in 2018. Hourly averages were calculated according to the European Monitoring Evaluation Programme/European Environmental Agency air pollutant emission inventory guidebook 2016 and were processed using AERMET View and a terrain pre-processor, AERMAP. For the model, the sources of pollution were the vehicles traveling on the road segment. The source was a line volume with 20 m of width and 2 m of height. The estimation methodology covered exhaust emissions of NO_x, SO₂ and PM contained in the fuel.

Results: The simulations provided average hourly, daily and annual concentrations of the different pollutants: 71.91 μg/m³, 42.41 μg/m³,11.23 μg/m³ for SO₂; 16.78 μg/m³, 9.89 μg/m³, 2.46 μg/m³ for NO_x and below the detection limit, 0.62 μg/m³, 0.15 μg/m³ for PM, respectively. These results indicate that on the National Road N2 in Togo, the concentrations of SO₂ were high compared to those of NO_x and PM. The daily average concentration of SO₂ was twice the permissible limits set by the WHO.

Conclusions: Emissions obtained from the AERMOD for NO_x and PM were less than the permissible limits set by the WHO, while the rate of SO₂ was twice the permissible limit. The fuels used on this road were very rich in sulfur. The sulfur level in fuels must be monitored by stakeholders in Togo.

Competing interests: The authors declare no competing financial interests.