The selection of Grand Lomé as the study area is based on three considerations. From a scientific standpoint, it is the main municipal solid waste generation area in Togo and encompasses a diversity of urban, peri-urban, residential, commercial and industrial municipalities representative of national waste-management challenges. From an environmental standpoint, waste management there combines several disposal pathways (landfilling, open burning, uncontrolled dumping), and the district hosts the Aképé Technical Landfill Center (CET), which provides the type of disposal infrastructure required to apply the IPCC first-order decay (FOD) method. The average household waste generation rate in Grand Lomé is estimated at 0.56 to 0.65 kg/capita/day [11]. From a methodological standpoint, the district benefits from statistical and operational monitoring that provides the activity data required for the estimates. Grand Lomé is therefore among the priority areas of national policies on sustainable waste management and SLCP reduction, within the framework of Togo’s Nationally Determined Contributions (NDCs). The locations of Grand Lomé and the Aképé CET are presented in Figure 1.

2.2.1. Sources and Scope

Table 1 presents the main activity data used to estimate SLCP emissions in Grand Lomé over the period 2021-2025. Demographic data were obtained from the National Institute of Statistics and Economic and Demographic Studies (INSEED), while data on waste generation and management were obtained from the National Agency for Sanitation and Public Health (ANASAP) and from the Directorate of Technical Services of the Autonomous District of Grand Lomé (DST-DAGL). Data from the technical services directorates of the thirteen municipalities were also used to complement the information on waste management. Taken together, these data document trends in population, daily per capita waste generation, quantities generated and landfilled, and the waste flows associated with each management pathway. The reported management pathways do not necessarily account for the entire generated waste stream, as additional fractions may be recovered, recycled or managed through other pathways not explicitly quantified in this study.

Figure 1. Location of the DAGL and the Aképé CET.

Table 1. Activity data.

For the FOD calculation, historical waste-disposal data preceding the study period were also used to initialize the decay model. The historical activity data used for this initialization are presented in Table 2.

Table 2. Historical waste-disposal data used for FOD model initialization.

2.2.2. Field Survey for the Estimation of Pfrac

The household survey used to estimate the fraction of the population practicing open burning (Pfrac) was conducted in 2025. A random sample proportional to the population of the thirteen municipalities of Greater Lomé was selected using the RGPH-5 population data [12], with a minimum of 18 households per municipality. A total of 800 households were surveyed, of which 756 questionnaires were usable (94.5%). The survey estimated that 41.67% of the population practiced open burning (95% CI: 38.2% - 45.2%). The resulting Pfrac value was applied consistently to each year of the 2021-2025 study period to estimate the annual quantity of waste burned under the local approach.

2.2.3. Waste Sampling and Physical Characterization

Waste sampling was carried out in proportion to the tonnages delivered from the various municipalities. Composite samples were characterized according to the MODECOM approach of ADEME, based on the AFNOR standard XP X30-408, with sorting into three particle-size classes (coarse: >100 mm; medium: 20 - 100 mm; fines: <20 mm), and then classified into eleven waste categories: food waste, green waste, disposable nappies, paper and cardboard, wood, textiles, plastics, rubber and leather, metals, glass and other waste. Sampling and characterization were carried out over the period 2021-2025. Four characterizations were performed each year, and annual mean values were calculated.

The composition of municipal waste obtained from delivery records was used as a proxy for the composition of household waste considered to be burned under the local approach. This represents an extrapolation because the waste samples were collected from municipal waste deliveries rather than directly at household burning sites.

The estimation of SLCP emissions is based on the IPCC 2006 Guidelines and their 2019 Refinement, implemented using the official “IPCC Waste Model Template”, which applies the first-order decay (FOD) method for methane emissions from landfilling. Emissions were estimated for the three main waste management pathways of Grand Lomé: landfilling, open burning and biological treatment. The pollutants considered are methane (CH₄) and black carbon (BC), treated as the short-lived climate pollutants of interest, together with carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x), which are accounted for as air pollutants and tropospheric ozone precursors.

All emissions are calculated using the general IPCC inventory equation:

where AD is the activity data, EF is the emission factor, i is the pollutant type, j is the management pathway and k the waste category.

2.3.1. Waste Landfilling (First-Order Decay Method)

Methane (CH₄) emissions from the landfilling of municipal solid waste were estimated using the first-order decay (FOD) method.

To account for the delayed decomposition of waste deposited before the study period, the FOD model was initialized using historical waste-disposal data for 2018-2020. These data were used to establish the initial stock of degradable organic carbon (DDOC) entering the 2021-2025 simulation period. The undecomposed DDOC remaining at the end of each year was carried forward to the following year according to the first-order decay constant (k). Consequently, the methane emissions estimated for 2021 include the contribution of waste deposited during the pre-2021 initialization period, in addition to waste deposited in 2021. Waste deposited before 2018 was not included because corresponding historical activity data were not available.

In the local FOD calculation, all waste quantities considered as landfilled were allocated to the Aképé Technical Landfill Center (CET), classified as a managed anaerobic solid waste disposal site. Accordingly, 100% of the landfilled waste was assigned to the managed anaerobic category (MCF = 1.0). This allocation was applied consistently over the modeled period. All variables were expressed in tonnes to ensure that the calculations were consistent with the activity data. For the local FOD calculation at the Aképé CET, the methane fraction in landfill gas was set to F = 0.50 . No methane recovery was considered during the study period ( CH 4 , recovered = 0 ), and the methane oxidation factor was set to OX = 0.

The degradable organic carbon potentially available for decomposition (DDOCm) is calculated as follows:

where W is the mass of landfilled waste (t), DOC is the degradable organic carbon content of the waste, DOC_f is the fraction of DOC that decomposes, and MCF is the methane correction factor accounting for the landfilling conditions.

The decomposition rate of the organic matter is described by the kinetic constant k, calculated as:

where t_1/2 denotes the half-life of the degradable organic carbon, which depends on climatic conditions and waste composition.

The amount of organic carbon actually decomposed during year T is then estimated by:

where DDOC_m(T-1) represents the stock of degradable organic carbon accumulated at the end of the previous year.

The amount of methane generated is obtained as follows:

Net methane emissions are then calculated after accounting for methane recovery and oxidation:

where CH 4 , generated , T is the amount of methane generated in year T , CH 4 , recovered , T is the amount of methane recovered in year T (t CH₄ year⁻¹), and OX_T is the methane oxidation factor. This formulation follows the structure implemented in the IPCC Waste Model Template, in which methane recovery is accounted for before applying the oxidation factor. The waste-fraction parameters used in the FOD calculation are presented in Table 3, while the methane correction factors associated with the disposal-site typology are presented in Table 4.

Table 3. Default parameters adopted per waste fraction (FOD model and open burning).

Table 4. Typology of disposal sites in Grand Lomé and methane correction factors (MCF) adopted.

n.a. = not applicable.

2.3.2. Open Burning

Unlike landfilling, open burning generates emissions directly during waste combustion, in the absence of any control device. This pathway is a source of CH₄, BC, CO, NMVOCs and NO_x. The annual amount of waste burned in the open (IW) is estimated by:

where P is the population of the DAGL, Pfrac is the fraction of the population practicing open burning, MSWP is the daily per capita waste generation (kg/capita/day) and Bfrac is the fraction of waste actually burned. Emissions by pollutant and by waste fraction are then calculated by:

where E ( i , k ) is the emission of pollutant i from waste fraction k, IW_i is the quantity of fraction k actually burned and E F ( i , k ) is the corresponding emission factor (kg/tonne of waste burned). The emission factors adopted are presented in Table 5.

Table 5. Emission factors adopted for the open burning of waste.

2.3.3. Biological Treatment

In Grand Lomé, composting is the dominant biological treatment, whereas anaerobic digestion remains marginal; only the organic fractions (food waste and green waste) are composted. N₂O emissions were not considered, since the study focused on short-lived climate pollutants. The associated CH₄ emissions are estimated by:

where M is the mass of organic waste treated (t) and EF is the emission factor. In line with the approach adopted for the other pathways, two emission factors were compared: the IPCC default value of 4 kg CH₄/t of waste treated, and a local value of 2 kg CH₄/t of waste treated. In the local approach, the mass of waste treated was expressed on a dry-matter basis, that is, adjusted for the moisture content measured locally, whereas the IPCC default factor applies to waste on a wet-weight basis.

The climate impact of each pollutant was converted into CO₂ equivalent (CO₂-eq) using the 100-year global warming potential (GWP-100), according to the standard IPCC formula:

The GWP-100 values adopted are 27.9 for CH₄ and 900 for black carbon (BC), the latter corresponding to a central scenario. Since the climate budget varies appreciably with the GWP metric adopted, a sensitivity analysis was conducted on this parameter. CO, NMVOCs and NO_x are reported only in t/year, as indicators of air-pollution and ozone-precursor co-benefits, because no harmonized GWP-100 value is currently recommended by the IPCC for these pollutants.

The uncertainty associated with the emission estimates was assessed in order to evaluate the representativeness of the results and to identify the parameters that govern the climate budget. The analysis was conducted separately for CH₄ emissions from landfilling, emissions from open burning and their conversion into CO₂-eq. The uncertainty values adopted for the parameters of the landfilling model are based on the 2019 Refinement to the IPCC Guidelines [14].

For landfilling, the analysis covers the following parameters: the quantity of waste deposited (MSWT), the fraction destined for landfilling (MSWF), the degradable organic carbon (DOC), the decomposable fraction of DOC (DOCf), the methane correction factor (MCF), the methane fraction in the biogas (F) and the degradation constant k. The uncertainties of the multiplicative parameters were combined by quadratic propagation according to the equation:

where U_C denotes the combined relative uncertainty and U_i is the uncertainty of parameter i. The parameters and uncertainties adopted for the sensitivity analysis are presented in Table 6.

Table 6. Parameters and uncertainties used for the sensitivity analysis of the landfilling model.

For open burning, CH₄ and BC emissions were recalculated at the two bounds of the Pfrac interval, with the other parameters held constant.

Finally, the sensitivity of the climate budget to the choice of the GWP-100 value for BC was assessed. The GWP of 900 used in the main analysis was compared with other values, in particular the value of 342 proposed by [15], in order to quantify the effect of the choice of climate metric on the final budget.

The total quantity of waste generated in Grand Lomé increased from 426,999 t/year in 2021 to 555,847 t/year in 2025, i.e., an increase of 30.2%. Over the same period, the quantities destined for landfilling rose from 256,200 to 389,093 t/year (+51.9%), while the quantities estimated to be burned in the open increased from 106,732 to 138,973 t/year. This trend reflects population growth and the gradual expansion of waste collection services.

The composition of waste in Grand Lomé also departs from the IPCC default profiles (Table 7). In 2025, the main fractions identified are green waste (26.3%), plastics (22.8%), food waste (11.8%) and textiles (4.5%), whereas the IPCC default profile adopted in this study assigns 53.9% to food waste, 6.4% to plastics and 0% to green waste. The urban context of Grand Lomé partly explains this discrepancy: gardening and green-space maintenance residues are abundant, and diets rely on fresh produce. Conversely, the relatively low proportion of food waste may reflect local biowaste management practices.

Table 7. Waste composition in Grand Lomé (2021-2025).

Compared with previous work, the share of plastics has more than doubled, whereas it did not exceed 11% in the earlier characterization of Lomé [10]. Likewise, the combined share of green waste and food residues reaches approximately 38.1% in 2025 in the present study, compared with 22% in the work of Koledzi et al. (2011) [10]. These differences may be explained by the recovery of plastic bottles along the collection chain and by changes in waste composition between the study periods.

CH₄ emissions associated with landfilling increased from 1090 t/year in 2021 to 4662 t/year in 2025,i.e., an increase of 327.7%. This increase exceeds that of the total quantity of waste generated (+30.2%) and that of landfilled waste (+51.9%). The discrepancy arises because emissions do not follow tonnage growth alone, but also depend on the nature of the landfilled waste and on the parameters governing its methanogenic potential, in particular the organic carbon content and the degradation dynamics. Among the waste management pathways, landfilling is the main source of CH₄ in Grand Lomé (Figure 2). Open burning is the second-largest emitting pathway in the sector, and the resulting emissions increased by approximately 30% between 2021 and 2025 for all pollutants studied: CH₄ (+30.2%), BC (+30.4%), CO (+30.2%), NMVOCs (+30.2%) and NO_x (+30.2%). Emissions therefore increase approximately in proportion to the quantity of waste burned. In 2025, CO reaches 5281 t/year and NMVOCs 3141 t/year, i.e., 10.4 and 6.2 times the CH₄ emissions (509 t/year), respectively; BC amounts to 90 t/year. The emission profile of this pathway is thus dominated by products of incomplete combustion.

Composting, by contrast, contributes only marginally to the estimated emissions: the associated CH₄ emissions increase from 2.95 to 4.24 t/year between 2021 and 2025, which is negligible compared with those from landfilling and open burning. In terms of source ranking, landfilling dominates CH₄ emissions, whereas open burning dominates BC, CO, NMVOCs and NO_x emissions.

Figure 2. Trends in SLCP emissions in Grand Lomé: CH₄ by management pathway (a) and pollutants from open burning (b), 2021-2025.

A small number of African studies provide points of comparison for the present results. In South Africa, [16] estimated CH₄ emissions from a landfill site at 6363.43 t/year. The estimate obtained for Grand Lomé is approximately 26.7% lower. In Cameroon, Paddy et al. (2025) [17] estimated 21.33 Gg of CH₄ over the period 2010-2030. For a given management pathway, the emission level remains closely dependent on the quantities landfilled, the composition of the waste stream and the emission parameters adopted.

For open burning, the emission profile obtained, dominated by products of incomplete combustion, with CO and NMVOCs greatly exceeding CH₄ and BC, is consistent with the findings of Das et al. (2018) [18] in five municipalities of Nepal. For 7400 tonnes of waste burned in 2016, the authors estimated 630 t/year of CO, 112 t/year of NMVOCs, 30 t/year of CH₄, 25 t/year of BC and 19.2 t/year of NO_x. In Grand Lomé, emissions are higher, owing to a burned waste stream almost twenty times larger. At the national level, Togo’s first biennial update report indicates, for the year 2017 and for the entire national territory, 4.23 Gg of CH₄ for solid waste disposal and 0.84 Gg of CH₄ for open burning, as well as 6.33 Gg of CO, 0.14 Gg of NMVOCs and 0.36 Gg of NO_x from open burning [19]. Despite the different spatial scopes and inventory periods, the same waste management issues emerge. Agbossou et al. (2022) [20] also showed that CH₄, NO_x and BC are, respectively, the first, second and third most emitted of these pollutants. Emission levels differ between studies depending on meteorological conditions (temperature and precipitation), the heterogeneity of the waste burned and the input data used.

The discrepancies between the local approach, based on the physical characterizations and the household survey conducted in Grand Lomé, and the IPCC default approach (Tier 1) vary from one pathway to another. For CH₄ from landfilling, the difference between the local approach and the IPCC approach is negative over the whole period: the local estimate is 42.3% lower in 2021 (1090 versus 1889 t/year), 45.8% to 56.9% lower over 2022-2024 and 44.4% lower in 2025 (4662 versus 8384 t/year), i.e., a mean deviation of −47.7% over 2021-2025. For open burning, the local approach estimated 509 t/year of CH₄ and 90 t/year of BC in 2025, compared with 819.5 t/year of CH₄ and 145.5 t/year of BC under the IPCC default approach, corresponding to approximately 37.9% lower emissions under the local approach (Figure 3). Over 2021-2025, the IPCC estimates increase from 629.4 to 819.5 t/year for CH₄ and from 111.8 to 145.5 t/year for BC, compared with 391 to 509 t/year and 69 to 90 t/year, respectively, under the local approach.

Figure 3. Comparison of emissions estimated under the local approach and under the IPCC approach (CH₄ from landfilling, CH₄ and BC from open burning), 2021-2025.

The discrepancies observed for CH₄ from landfilling are related to waste composition: the reduced share of food waste (11.8%) and the share of green waste (26.3%) and plastics (22.8%) in the local approach alter the amount of degradable organic carbon introduced into the FOD model and lower the estimate relative to the default approach. For open burning, since the emission factors are identical in both approaches, the discrepancy arises from the activity data. The local estimate indicates that 41.67% of the population practiced open burning, whereas the default approach assumes that the entire population not served by collection burns its waste, in addition to the waste burned by the served population, which raises this proportion to 67%. In 2025, the local approach estimated 138,973 tonnes of waste burned, compared with 223,897 tonnes under the IPCC default approach, corresponding to a 37.9% lower activity level under the local approach. Because the same emission factors were used for the corresponding pollutants, this difference in activity data directly affects the estimated CH₄ and BC emissions from open burning. The value of the local approach lies both in the magnitude of the deviation from the default approach and in the representation of the underlying emission mechanisms. Rather than being inherently more accurate, local data provide estimates that are more specific to the waste composition and management practices observed in Grand Lomé: they quantify the extent of household burning and account for a waste composition that differs from the regional default profile.

The climate impact reaches 225.4 Gg CO₂-eq in 2025, compared with 103.5 Gg CO₂-eq in 2021, i.e., an increase of 117.8%. The climate pressure exerted by the sector is increasing, and the distribution among pathways is shifting (Figure 4). Open burning dominates at the beginning of the period, whereas landfilling becomes the main source by the end of the period, with its share rising from 29.4% in 2021 to 57.7% in 2025. Conversely, the contribution of open burning, considering CH₄ and BC, decreases from 70.5% to 42.2%. This relative decline reflects the faster increase in the impact associated with landfilling. Composting contributes only marginally to the estimated climate impact, below 0.1% over the whole period, since its associated CH₄ emissions are very small compared with those from landfilling and open burning.

Figure 4. Trends in the climate impact of the waste sector, by pollutant (a) and by management pathway (b), 2021-2025.

The growing predominance of landfilling is associated with the increasing quantities of waste delivered to the Aképé CET and with their progressive degradation, which is liable to generate methane. CH₄ from landfilling now accounts for most of the increase in the climate budget. Reducing these emissions would require, in particular, controlling the amount of organic matter landfilled and capturing, recovering and treating the biogas. Although open burning emits a smaller mass of CH₄ than landfilling, the presence of BC increases its relative climate importance. Between 2021 and 2025, the impact associated with CH₄ from open burning increases from 10.9 to 14.2 Gg CO₂-eq, whereas that attributed to BC increases from 62.1 to 81.0 Gg CO₂-eq. Within open burning, BC is the dominant contributor. Across the three pathways, its contribution to the total climate impact decreases from 60.0% in 2021 to 35.9% in 2025.

The increase in the climate impact is also accompanied by a rise in per capita intensity, which increases from 48.66 to 96.2 kg CO₂-eq/capita between 2021 and 2025, i.e., an increase of 97.7% (Figure 5).

Figure 5. Trends in the per capita climate impact of the waste sector (2021-2025).

The propagation of the uncertainties associated with the multiplicative parameters of the FOD model results in a relative uncertainty of ± 52.2% for CH₄ emissions from landfilling. This is comparable to the value of ±50% adopted by default when the available data are limited [1]. For open burning, accounting for the 95% confidence interval of Pfrac (38.2% - 45.2%) results in a variation of −8.3% to +8.5% in CH₄ and BC emissions (Figure 6). The influence of this parameter on the central estimate therefore remains limited.

A second source of uncertainty concerns the GWP-100 value for BC. When this value varies from 100 to 1700 [3], the total climate budget varies from 153.4 to 297.4 Gg CO₂-eq. Furthermore, the use of a GWP of 342 [15] reduces the budget by 22.3% relative to the main scenario based on 900. The climate importance attributed to BC therefore depends strongly on the metric adopted.

The absence of direct measurements of CH₄ emissions at the Aképé CET and of BC from open burning limits the experimental validation of the estimates. The main sources of uncertainty differ according to the emission pathway and the climate metric adopted: the estimation of CH₄ from landfilling is mainly limited by the parameters of the FOD model, whereas the climate assessment of BC is sensitive to the GWP-100 value adopted.

Figure 6. Sensitivity of CH₄ (a) and BC (b) emissions from open burning to variation in Pfrac.

Emissions from the waste sector of Grand Lomé constitute a short-term climate issue, driven by CH₄ generated by landfilling and by BC from open burning. The main mitigation options are twofold and complementary. The first is the elimination of open burning, for which the extension of collection is a prerequisite; it simultaneously addresses BC, CO, NMVOCs and NO_x emissions and offers potential health co-benefits. The second, which becomes increasingly important for climate mitigation over the period, is the reduction of methane generation from landfilled waste through the diversion of the organic fraction and the modernization of landfilling combined with biogas capture. Sorting and recovering recyclable waste acts on both pathways.

Studies carried out in Gulu and Kisumu have shown that the extension of collection is among the priority measures, since it led to emission reductions there [21][22]. In Grand Lomé, the scale of the problem is substantial: an estimated 138,973 t of waste were burned in the open in 2025.

Reducing open burning remains a major mitigation lever: this pathway accounted for 70.5% of the climate impact of the sector in 2021 and still 42.2% in 2025, with BC alone representing 35.9%. The progressive elimination of this practice would reduce BC emissions as well as those of other air pollutants (NMVOCs, CO, NO_x), thereby providing both climate and health co-benefits. A review of 170 publications from Asia and Africa by [23] identified the persistence of open burning as one of the main obstacles to the effectiveness of waste management systems in developing countries.

The diversion of the organic fraction directly targets the leading source of the sector: composting and anaerobic digestion reduce the amount of biodegradable matter liable to produce CH₄ in landfills. Its implementation nevertheless requires separate collection of biowastes, treatment capacity commensurate with the flows concerned, and outlets for the compost produced.

Improved landfill management and biogas capture apply specifically to the Aképé CET. The estimates presented assume that all the CH₄ generated is emitted after partial oxidation in the cover layer. Equipping the site with a capture network, coupled with energy recovery or, failing that, with controlled flaring, would act directly on the leading emission source of the sector.

Source separation and the recovery of recyclables complement these levers by acting on both pathways simultaneously. The high share of plastics in the waste stream (22.8% in 2025) indicates a recoverable flow whose diversion would simultaneously reduce the mass landfilled and the mass burned.

Finally, the implementation of these measures remains contingent on the availability of financing, infrastructure development, the strengthening of institutional capacity and changes in household behavior.