**1. Introduction**

It is estimated that over 40% of the world's population is currently relying on solid-fuels for cooking and heating [1]. According to the World Health Organization (WHO), the inefficient utilization of biomass and coal for these purposes constitutes today's largest global environmental health risk [2,3]. Worldwide, over 4 million deaths occur per year from illnesses related to the smoke from solid-fuel combustion indoors, which mainly affects women and children [4,5]. In developing countries, wood and charcoal continue to play a vital role in meeting household energy demands, where it remains easily accessible and affordable [6–8]. Thus, the transition to cleaner cooking fuels in advanced cookstoves

constitutes an important way to address several of the 17 Sustainable Development Goals (SDGs) [9,10], contributing to address at least five of the SDGs, including the: (1) Good health and well-being (SDG 3); (2) Gender equality (SDG 5); (3) A ffordable and clean energy (SDG 7); (4) Climate action (SDG 13); and (5) Life on land (SDG 15).

In Sub-Saharan Africa (SSA), only 35% of the population have access to electricity and 80% of the people rely on traditional firewood, charcoal, animal dung and agricultural residues for cooking [11,12]. Negative environmental impacts such as global warming due to the emission of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), eutrophication related with the emission of nitrogen oxides (NOx) and N2O, acidification associated with the emission of sulphur dioxide (SO2) and NOx, and toxicological e ffects on humans related with the emission of NOx and particulate matter (PM) are potentially intensified by traditional cooking. In Kenya, the cooking sector emissions are driven by rapid population and economic growth [13], and household air pollution (HAP) causes 15,600 deaths with direct impacts on the health of around 15 million people [14–17].

In the Kenyan context, the transition to advanced cookstoves using upgraded biomass fuels (e.g., wood pellets and biogas) produced via renewable energy strategies constitutes a relevant way to mitigate HAP. Such locally produced biofuels based on waste valorization and agroforestry strategies have a grea<sup>t</sup> potential to enhance land restoration and livelihoods, as agroforestry is a powerful tool to enhance multiple ecosystem services [18]. Famers in Kenya are responsible for producing a substantial part of the food consumed in the region. In this context, an integrated managemen<sup>t</sup> of crop-residues at the farm scale can tackle challenges of food security, poverty and climate change [18,19]. Furthermore, the utilization of crop-residues remains an opportunity for sustainable bioenergy production in rural and peri-urban communities [20]. In such a perspective, the Kenyan governmen<sup>t</sup> has worked on designing proper strategies towards the deployment of e fficient bioenergy systems [21,22], including the use of both agricultural crop [23] and industrial biomass residues [21] for the production of biogas and densified biomass fuels. The Kenya Country Action Plan (CAP) for Clean Cookstoves and Fuels has established a target to promote the installation of cleaner cookstoves in 5 million households by 2020 [24]. With a thermal e fficiency over two times higher than that achieved by improved cookstoves using wood-logs and sticks [25,26], advanced biomass cooking solutions such as micro-gasifier and biogas cookstoves can be key in technologies to address such clean cooking systems.

Despite the existing initiatives, there is currently a knowledge gap on how to design sustainable cooking strategies in the context of emerging circular bioeconomies. Few studies have analyzed the life-cycle environmental impact of integrated biomass fuel/cookstove strategies on the mitigation of HAP at the sub-national level. Various studies have been analyzed the impact of di fferent energy transition options [8,27,28]. In Western Kenya, Carvalho et al. [26] have applied the Long-Range Energy Alternative Planning (LEAP) software to analyze the energy savings and emissions caused by distinct bioenergy strategies on HAP in Kisumu County. The study was applied for the time span between 2015 and 2035, showing part of the environmental benefits of such strategies. Although the previous energy modelling study [26] shows the HAP mitigation potential at the sub-national level, there is currently a limited number of studies assessing the overall environmental performance of these transitions in a life-cycle assessment (LCA) perspective.

As defined by the International Standard Organization (ISO) in the ISO 14040 [29], LCA is a technique used to quantify the environmental impacts of a product system like a cooking fuel over its whole life cycle, from raw material acquisition through production, use, end of life, treatment, recycling, and disposal [29]. A previous LCA study conducted in Kenya observed that biogas from animal dung and ethanol from wood as cooking fuels had the best environmental performance in almost all environmental impact categories while charcoal briquettes from wood exhibited poor environmental performance due to emissions resulting from kiln operation [30]. Okoko et al. [31] confirmed the higher carbon footprint of unimproved charcoal value-chain in relation to alternative biomass energy solutions for cooking in Kenya and Tanzania. Lansche and Müller performed a comparative LCA on traditional biomass and biogas household cooking systems in Ethiopia, demonstrating the high potential for environmental improvements when adopting biogas systems. Although the previous LCA studies analyzed the environmental impacts of alternative cooking value-chains in a certain static moment in time, they did not include a LCA considering regional energy forecasts, i.e., a dynamic LCA approach [32]. The dynamic LCA method can be applied to analyze environmental impacts in di fferent time spans. Pehnt [33], for instance, considered the time-variation of electricity mix in the assessment of GHGs and acidification impacts. García-Gusano et al. [34] combined energy forecasts using LEAP with a dynamic LCA approach to evaluate the e ffects of various coal power plant retrofits over time. Although various dynamic LCA studies conducted, there is currently a lack of approaches dedicated to analyzing household energy transitions in the developing region context.

In the present research, a dynamic LCA based data provided by a previous energy forecast study [26] is conducted to determine the environmental sustainability of emerging biomass cooking strategies in the Kisumu County (Western Kenya). Although most biomass cookstoves have not progressed to the point that they are equivalent to Liquefied Petroleum Gas in terms of e fficiency and cleanliness in the household indoor environments [35], this study is confined to evaluate the advances in the local use of biomass resources in the context of renewable energy and bioeconomy transitions. WIth this background, the present work constitutes not only an LCA of alternate biomass value-chains, but also a methodological development in the integration of LEAP/LCA tools for the analysis of the environmental sustainability of distinct energy policies. Despite the fact that several studies have conducted life-cycle analysis of products and systems at the country [34,36] and city levels [37,38], few have combined integrated energy models with LCA to evaluate the environmental impact of energy policy scenarios at the sub-national level. The Kisumu County in Western Kenya was selected for the case study as it presents a large availability of endogenous biomass resources, including agricultural and industrial residues that can potentially be used for the production of cooking biofuels. The region presents an important area of fertile agricultural land that may serve for the establishment of local-based agroforestry systems [39,40], which can be used to produce wood fuel in a more sustainable and resilient manner.
