Determination of the Types of Air Pollutants Prepondering in the City of Lome in Togo (West Africa)

The increase in the urban population and the high concentration of many anthropogenic activities in certain regions of the world lead to atmospheric disturbances. The excess concentration of several chemical elements leads to air pollution. In order to identify the types of air pollutants, a study was carried out in the city of Lomé, the capital of Togo. The objective of this study is to achieve a better knowledge of the types of air pollutants in the city of Lomé. The identification of the various atmospheric pollutants linked to the sources of pollution was made using micro-sensors. The standardized method was used to access target gas concentration levels. The average concentrations of NO2 gaseous pollutants at landfills are on average 0.333 μg/m3; 0.403 mg/m3 at the industrial level, at the transport level they are on average 0.434 mg/m3 for the morning and 0.457 mg/m3 for the evening. Concentrations of carbon dioxide (CO2) are higher in industrial areas than in others sources of pollution. The average concentration measured at this level is 1632.79 mg/m3. In terms of road transport, in the mornings the average concentration is 1493.23 mg/m3, in the evening the average concentration is 1354.09 mg/m3. On the other hand, they are lower at the level of the landfills, the average of which is 1265.08 ppm. The highest SO2 concentrations are also observed only in the landfills of Port 1 and Bè_Kpota 2 with concentrations respectively and relatively low and equal to 0.081 mg/m3 and 0.1616 mg/m3. The concentration of ground-level ozone is zero in industries and landfills. On the other hand, at the level of road transport, some values were recorded at the level of two road transports. These are Carrefour Attikoumé Djidjole (17.03 mg/m3) and Carrefour 2 Lions How to cite this paper: Atator, L.T., Kamou, H., Bawa, A., Agbodan, K.M.L., Polo, A.A., Pereki, H., Akpavi, S.B. and Akpagana, K. (2021) Determination of the Types of Air Pollutants Prepondering in the City of Lome in Togo (West Africa). Atmospheric and Climate Sciences, 11, 729-748. https://doi.org/10.4236/acs.2021.114043 Received: August 8, 2021 Accepted: October 24, 2021 Published: October 27, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
Human activities such as automobile traffic, industrial activities, and massive urbanization are considered to be the main sources of emissions of gaseous and particulate pollutants into the air and their significant concentrations measured in urban environments [1] [2] [3]. In major cities in Europe, Asia and North America, air quality monitoring networks are installed with the aim of informing the public authorities and the population in real-time about the different levels of air quality pollution. The studies carried out in these cities underline the urgency of taking measures to reduce the emissions of pollutants into the atmosphere in order to mitigate the impacts on health and the environment [1] [4]. Air quality has received special attention in recent decades. This follows the steady increase in air pollution recorded around the world, resulting in the release into the atmosphere of toxic elements mainly of anthropogenic origin. This causes obvious and significant degradation of the environment and ecosystems [4]. In addition, the ever-increasing development of new technologies has been accompanied by intense industrial, agricultural, commercial and transport activities, promoting a strong rural exodus, particularly in the emerging countries of the South. These are the determining factors of atmospheric pollution in large urban agglomerations that have required phytosanitary studies in order to assess the consequences that toxic pollutants can generate. These pollutants diffused into the atmosphere are constantly captured by plants [5]. In Togo, the city of Lomé is not immune to the problem of air pollution. The air is now in an alarming state in terms of its quality. The increase in air pollution recorded is mainly due to the operation of factories and the lack of public transport, the use of dilapidated vehicles, highly polluting two-stroke mopeds and the sale of illegal gasoline on the sides of the tracks. The objective of this study is to determine the predominant types of air pollutants in the city for better plant biomonitoring and air quality.

Area Study
The study was conducted in the city of Lomé, the capital of Togo, located in the southwestern tip of the coastal sedimentary basin also called the maritime coastal plain of Togo, between longitudes 1˚11' and 1˚17' East and latitudes 6˚06' and 6˚12' North. Biogeographically, it is located in ecological zone V [6]. It is limited  to the south by the Atlantic Ocean, to the west by Ghana and the old Kpalimé   rails, to the north by street 345 which passes in front of the Agbalepédogan bus   station, the boulevard of the new presidency, the road of Togolese Football Federation-Togo 2000

Data Sampling
The measurement of atmospheric pollutants linked to the identified sources of pollution was made using micro-sensors (Table 1). The standardized method adopted by [7]. Zaher Al Barakeh, 2012 was used to access the concentration levels of the targeted gases with a high precision corresponding to specific quality objectives. For this study, the 500 series aeroqual sensors equipped with a removable monitor were used. The gases emitted being transported in the direction of the wind, the measurements were carried out according to the direction of the wind at each source. The time ranges for measurements differ from one source to another. Table 2 shows the time slots for the various measurements taken. For each of the sources, the measurements were carried out in no more or strong wind at a temperature of 29˚C to 33˚C and relative humidity is between 60.6% -80.00%.

Data Analyses
Data were entered by type of anthropogenic source and subjected to descriptive analysis using Excel spreadsheets. The quantities of pollutants were calculated by station.

Variation of Different Types of Pollutants at Industry Level
The difference between the different variations of CO 2 at the industry level is not

Discussion
This chapter presents the concentrations of the various atmospheric pollutants, in particular carbon dioxide (CO 2 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), carbon monoxide (CO) and ozone (O 3 ) measured at the level of the main sources of atmospheric pollution in the city of Lomé. In fact, these same pollutants have been reported in several cities in African countries and around the world. These include [4] in Ivory Coast; [8] in Beirut and Lebanon; [9] in Benin; [10] in it is port activities and heavy traffic that are likely to emit NO 2 that could explain these concentration levels. According to the work of [11], these activities in industrial zones are well known to be the main source of anthropogenic nitrogen oxide emissions into the atmosphere. In addition to road transport sites, high concentrations were also measured at sites dominated by certain industries. This is notably the case of the Amina, Brewery and Sivop industries where the average concentration measured respectively is 0.556 ± 0.08; 0.520 ± 0.04; 0.505 ± 0.06. These high concentrations measured in Lomé at the level of road transport confirm that NO 2 is indeed a tracer of the traffic source as pointed out by [12]. Most vehicles are second-hand and are over 20 years old [9]. These vehicles, which for the most part no longer comply with the air quality standards in force in the states of the European Union (EU), are imported en masse and used in public transport because of their moderate prices. These same results were reported by [9].
In the city of Cotonou in Benin. In fact, in this city of Cotonou, unlike in Lomé, these are the industrial zones that record high concentrations of nitrogen dioxide (NO 2 ) followed by road transport. As in the case of NO 2 , the distribution of carbon dioxide (CO 2 ) concentrations in the city of Lomé is higher in industrial areas.
In In the morning the average concentration is 0.800 (max = 3.4; min = 0) and in the evening the average concentration is 0.838 (max = 2.602; min = 0.108). These results could indicate that the SO 2 here is mainly emitted from the road transport source. According to several authors, road transport can constitute an important source of SO 2 [17] [18]. In Côte d'Ivoire and Benin, the sulfur content of the fuel produced and marketed is greater than 2000 ppm [19]. This content is more than 40 times higher than the standards applied in most developed countries (50 ppm or less). For the majority of the Abidjan sites (85%) the average SO 2 concentrations are less than 2 ppb. The lowest concentrations were measured east of the city of Abidjan where the concentrations vary between 0.4 ppb and 1.1 ppb. The concentration of ground-level ozone is zero in industries and landfills. On the other hand, at the level of road transport, some values were recorded at the level of two road types of transports. These are Carrefour Attikoumé Djidjole (17.03) and carrefour 2 Lions (0.001). It is zero at the level of other road transport. Unlike in other countries such as Ivory Coast, Senegal, Ghana and Benin, overall the presence of O 3 is observed in all cities with concentrations ranging from 5.1 ppb to 19.1 and 5.1 ppb to 20.1 ppb. These sites benefit from atmospheric conditions favorable to the net production of ozone such as monthly sunshine [20] [21], high relative humidity of the air due to the presence of water vapor from the sea spray and the presence of biogenic from vegetation. The spatial distributions of carbon monoxide (CO) concentrations in the city of Lomé at the industry level are on average 22.57 (max = 7.71; min = 0); at landfills it is on average 0.24 (max = 1.34; min = 0). In terms of road transport, it is on average 7.890 (Max = 34.57; min = 0) for the morning and 8.23 (max = 27.82; min = 0.58) for the evening. In addition to other emissions, carbon monoxide emissions are higher at the level of industries in Lomé followed by road transport. The work of [22] has shown that the highest concentrations are recorded at the level of industries and road transport, but fortunately, there is a strong reduction in this gas.

Conclusion
This article reports on the measurements of gaseous pollutant concentrations carried out using passive sensors carried out during this study. These measurements carried out both in industries, at landfills and at road transport-level have highlighted the spatial distribution of gaseous pollutants (CO 2 , NO 2 , SO 2 , CO and