Direct exposure to household fine particulate air pollution (HAP) associated with inefficient combustion of fuels (wood, charcoal, coal, crop residues, kerosene, etc.) for cooking, space-heating, and lighting is estimated to result in 2.3 (1.6–3.1) million premature yearly deaths globally. HAP emitted indoors escapes outdoors and is a leading source of outdoor ambient fine particulate air pollution (AAP) in low- and middle-income countries, often being a larger contributor than well-recognized sources including road transport, industry, coal-fired power plants, brick kilns, and construction dust. We review published scientific studies that model the contribution of HAP to AAP at global and major sub-regional scales. We describe strengths and limitations of the current state of knowledge on HAP’s contribution to AAP and the related impact on public health and provide recommendations to improve these estimates. We find that HAP is a dominant source of ambient fine particulate matter (PM2.5) globally — regardless of variations in model types, configurations, and emission inventories used — that contributes approximately 20 % of total global PM2.5 exposure. There are large regional variations: in South Asia, HAP contributes ∼ 30 % of ambient PM2.5, while in high-income North America the fraction is ∼ 7 %. The median estimate indicates that the household contribution to ambient air pollution results in a substantial premature mortality burden globally of about 0.77(0.54–1) million excess deaths, in addition to the 2.3 (1.6–3.1) million deaths from direct HAP exposure. Coordinated global action is required to avert this burden.

This paper presents results from eight field studies in Asia and Africa on the emissions performance of 16 stove/fuel combinations measured during normal cooking events in homes. Characterizing real-world emissions performance is important for understanding the climate and health implications of technologies being promoted as alternatives to displace baseline cooking stoves and fuels. Almost all of the stove interventions were measured to have substantial reductions in PM2.5 and CO emissions compared to their respective baseline technologies (reductions of 24–87% and 25–80%, for PM2.5 and CO emission rates, respectively), though comparison with performance guidance from the World Health Organization (WHO) and the International Organization for Standardization (ISO) suggests that further improvement for biomass stoves would help realize more health benefits. The emissions of LPG stoves were generally below the WHO interim PM2.5 emissions target (1.75 mg/min) though it was not clear how close they were to the most aspirational ISO (0.2 mg/min) or WHO (0.23 mg/min) targets as our limit of detection was 1.1 mg/min. Elemental and organic carbon emission factors and elemental-to-total carbon ratios (medians ranging from 0.11 to 0.42) were in line with previously reported field-based estimates for similar stove/fuel combinations. Two of the better performing forced draft stoves used with pellets—the Oorja (median ET/TC = 0.12) and Eco-Chula (median ET/TC = 0.42)—were at opposite ends of the range, indicating that important differences in combustion conditions can arise even between similar stove/fuel combinations. Field-based tests of stove performance also provide important feedback for laboratory test protocols. Comparison of these results to previously published water boiling test data from the laboratory reinforce the trend that stove performance is generally better during controlled laboratory conditions, with modified combustion efficiency (MCE) being consistently lower in the field for respective stove/fuel categories. New testing approaches, which operate stoves through a broader range of conditions, indicate potential for better MCE agreement than previous versions of water boiling tests. This improved agreement suggests that stove performance estimates from a new ISO laboratory testing protocol, including testing stoves across low, medium, and high firepower, may provide more representative estimates of real-world performance than previously used tests. More representative results from standardized laboratory testing should help push stove designs toward better real-world performance as well as provide a better indication of how the tested technologies will perform for the user.

This paper presents results of three United States Environmental Protection Agency (U.S. EPA) sponsored field studies which assessed the fuel consumption impacts of household energy programs in Benin, Uganda, and Gujarat, India. These studies expand on a previous round of U.S. EPA supported efforts to build field testing capacity and collect stove performance data in Peru, Nepal, and Maharashtra, India. Daily fuel consumption estimates of traditional and intervention technologies were made using the Kitchen Performance Test (KPT) protocol to determine the potential fuel savings associated with the respective programs. The programs in Benin and Gujarat, India resulted in significant fuel savings of approximately 29% and 61%, respectively. In Uganda, the homes using liquefied petroleum gas (LPG) consumed approximately 31% less charcoal than those not using LPG, although the total energy consumption per household was similar between the baseline and LPG user groups.

Published data from quantitative assessments of in-home fuel use in developing countries are sparse, yet this information is important for understanding the basic daily energy consumption of half the world's population as well as the effectiveness of programs seeking to reduce the health, environmental, and socioeconomic impacts of using inefficient cooking technologies and fuels. This paper presents results from a coordinated training and field study program sponsored by the U.S. Environmental Projections Agency, with the goal of increasing our understanding of household energy use by building capacity of stove implementing organizations. The programs were conducted with stove organizations in India, Nepal, and Peru, with results from Nepal and Peru indicating the respective stove interventions resulted in significant fuel savings (~ 27–66%), and in India the energy consumption from combined usage of a pellet stove and liquefied petroleum gas was 59% lower than use of traditional biomass stoves. The fuel savings in Peru were highly dependent on the level of stove maintenance and user training with the largest savings (66% per capita) achieved in homes where the stoves were maintained and users were provided additional training, indicating that these are critical factors for realizing maximum stove performance in homes. Combining these results with previously published KPT results showed patterns of higher baseline fuelwood consumption in Latin America (2.1–3.4 kg per capita per day) in comparison to Nepal and India (1.0–1.4 kg per capita per day). The fuel savings estimates from the KPT studies were generally similar to savings estimates for controlled testing (Water Boiling Tests and Controlled Cooking Tests) of the respective program stoves, showing promise for better linking stove performance in the laboratory with field performance. Finally, variability of fuel consumption and fuel savings estimates are examined to inform on study design and monitoring for carbon offset methodologies.