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Around one-fourth of the global population lacks access to clean fuels and technologies for cooking, most of them living in low- and middle-income countries. Reliance on rudimentary and inefficient biomass cookstoves results in high pollutant concentrations that adversely affect the health of those exposed to indoor air pollution, the environment, and the climate. In this study, we systematically reviewed the literature on aerosol and particle properties from biomass cookstoves of relevance to health, climate and the environment. We identified 187 articles reporting aerosol characterization (i.e. particulate mass or number concentrations, or particle size distributions). Of these, 82 presented detailed particle characterization (e.g. chemical composition), thus selected for further analysis. Articles were classified based on the reported particle properties and the study type and location, which allowed mapping research efforts to date and identifying major knowledge gaps. Most reviewed studies (39 articles) on particle properties reported particulate organic and elemental carbon composition. Despite considerable variability, the EC/TC ratio generally varied in the range of 0.1-0.4 for all cookstove technologies, indicating that organic carbon is the dominating PM fraction in biomass cookstove emissions. Findings from this systematic review highlight the need for further studies on particle properties from biomass cookstoves that use a multidimensional approach simultaneously combining several properties and different cookstove-fuel combinations. We also assessed the policy landscape, including the three main global policies concerning biomass cookstove emissions, and evaluated whether those policies included the state of the knowledge on particle properties and their adverse effects on human health, climate, and the environment. We finally identify key aspects that future policies should integrate, and critical knowledge gaps that must be filled to advance the overall development of the field. Notable was that field studies consistently report particle emission factors (PM_2.5) higher than the ones determined under laboratory conditions, for example, an average of 8.9 g/kg_fuel (field) compared to 5.2 g/kg_fuel (lab) for traditional cookstoves and 4.0 g/kg_fuel (field) compared to 1.3 g/kg_fuel (lab) for advanced cookstoves. Cookstove manufacturers, practitioners, policymakers, and society in general will benefit from a solid knowledge base regarding particle properties from biomass cookstoves and their related adverse effects on human health, climate, and the environment.

Around 2.3 billion people lack access to clean cooking solutions worldwide. In sub-SaharanAfrica, over 80% of the population relies on rudimentary, low-efficiency, and highly pollutingcooking appliances. This study presents in-depth field data collected in rural Rwanda oncombustion and emission performance from four biomass cookstoves fueled with locally andsustainably produced woody biomass. The study builds on pairwise cookstove combinations,with two cookstoves tested in each of the six households included in the study.Our results show that the rocket stove and the two natural-draft gasifiers required less fuel tocook the same recipe. The cooking time was slightly increased for the natural draft gasifierscompared to the three-stone fire. Biochar yield ranged from 143-457 g/cooking event, with themost producing cookstoves being the gasifiers and 3-stone fine and the rocket stoves. Carbonmonoxide (CO) concentrations averaged up to around 180 ppm with peaks of up to 400 ppmwhen cooking with the three-stone fire. On the contrary, the lowest CO concentrations wereobserved when using the industry-manufactured gasifier, ranging from 7 to 14 ppm. AveragePM1 and particle number (PN) concentrations followed similar trends of reducedconcentrations along the technological gradient, except for the artisan-manufactured gasifier,which performed worse than the less technologically advanced rocket stove for bothparameters.We used a portable Scanning Mobility Particle Sizer (SMPS) to determine particle numberconcentrations and size distributions. The analysis showed that particle numberconcentrations were significantly higher for the 3-stone fire than for the other three studiedcookstoves. The analysis also shows that particle size distributions varied over time for all thecookstoves. In all cases, particle size distributions peaked around 80-100 nm, varying overtime during cooking events. Regarding specific particle properties, our study shows that,despite all the cooking events being performed with the same fuel, the particle propertieschanged considerably between cookstoves. We also show that improved cookstoves generatelower black and brown carbon (BC and BrC) emissions. The results show a significant CO,PM1, BC and BrC emission reduction from improved cookstoves compared to the three-stonefire. On the contrary, particle size distributions from artisan-manufactured gasifiers weresimilar to those from the three-stone fire. In addition, the detailed and source-specificinformation provided in this study will benefit cookstove manufacturers, modelers, andpolicymakers.Conclusively, improved cookstoves have a vast potential for reducing fuel consumption andemissions compared to the three-stone fire. This study provides valuable and comprehensivefield-based data on combustion and emission performances and aerosol and particleproperties.