To reduce in-home pollution, pay attention to improved ventilation

August 2023

We find that improved household ventilation in rural Senegal can reduce kitchen pollution levels by a similar amount as upgrading fuel and stove technology, once we account for real world cooking practices. The effects of ventilation alone are likely insufficient to deliver elusive health impacts, however, and should thus be seen as an interim step toward realizing the benefits of clean cooking.
Gunther Bensch, Marc Jeuland, and Jörg Peters
Despite considerable and commendable effort to promote clean stoves and fuels, the world is still far from achieving universal access to clean cooking by 2030, as outlined in Sustainable Development Goal 7. The challenge is especially great in sub-Saharan Africa (SSA). In rural SSA, 95 % of the population continues to rely primarily on traditional cooking with solid cooking fuels.

Air pollution in the home, and its consequences for health, is one of the major problems associated with traditional cooking. Interventions and policy discourse on this problem are today largely focused on promotion of clean stoves and fuels (e.g., electricity and liquefied petroleum gas), but adoption of such solutions by lower-income people is lagging. Meanwhile, policy discourse completely ignores the potential of other complementary interventions, such as improving kitchen ventilation.

While ventilation does not reduce emissions released from traditional cooking, our research shows that it can reduce kitchen pollution levels substantially, with the most extensive ventilation options reducing these levels similarly to the effects typically seen with changes in fuels and stove technology. Amid efforts to achieve universal access to clean cooking, we advocate for additional focus on policies and programs that leverage these benefits from improved ventilation.


The Pollution Burden of Traditional Cooking

Firstly, we find extremely high levels of average kitchen concentrations of particulate matter (PM2.5) during a 24-hour monitoring period, reaching nearly 500 μg/m3 (Figure 1). This exceeds even the least stringent WHO interim air quality target of 35 μg/m3 by more than one order of magnitude. Personal exposure measurements are substantially lower, but average 24-h personal exposure remains high (136 μg/m3 PM2.5). These measurements are based on small state-of-the-art optical sensors placed in over 100 kitchens and worn by around 200 household cooks in rural Senegal.

Fig. 1. Cumulative distribution of 24-hour mean PM2.5 kitchen concentration and personal exposure

Graph showing both kitchen concentration and personal exposure higher than WHO targets

The Role of Ventilation in Household Air Pollution

We also document a strong relationship between increased kitchen ventilation and kitchen pollution concentrations. By allowing harmful emissions to dissipate, improved ventilation leads to significantly lower kitchen levels of PM2.5 – and the magnitude of the reductions is similar to those typically achieved through the adoption of clean stoves and fuels. Figure 2 compares our findings with those a recent meta-analysis by Pope et al. (2021) on such stove and fuel interventions. The below figure shows results for single and composite indicators of kitchen ventilation derived from the following dimensions: (i) kitchen air exchange (wall structure, roofing structure, kitchen openings), (ii) kitchen volume, (iii) kitchen separation and (iv) ventilation behaviour.

Fig. 2. Reduction potentials for kitchen concentration compared to those from stove and fuel interventions

Graph comparing effects of ventilation with fuel intervention – in case of full ventilation, reduction in pollution greater than some fuel interventions

Note: The figure presents estimates for the two highest categories of kitchen ventilation (out of the four we defined in the above), where full ventilation represents open-air cooking and substantial ventilation is defined as, for example, a permeable roof structure with openings. LPG stands for liquefied petroleum gas and EEBC for energy-efficient biomass cookstoves.

Unravelling the Exposure Puzzle

While improved ventilation shows promise in curbing kitchen pollution, the link between ventilation and personal exposure to pollutants remains more complex. Somewhat surprisingly, we found that personal exposure did not significantly decrease with improved kitchen ventilation. This observation hints at the crucial role of cooking behaviour in shaping exposure outcomes. We speculate that cooks try to avoid or reduce smoke exposure during peak emission events, for example by leaving the kitchen periodically, or engaging in other smoke avoidance strategies. Notably, technology adoption studies from countries with similar cooking conditions and shares of clean fuel or chimney wood fuel stove usage find similar results on the relationship between kitchen pollution and personal exposure.

Ventilation and the Cooking Environment

These findings suggest several vital needs for future policy and research that aim to deliver cooking-related health benefits. To begin with, measuring ventilation and cooking behaviour systematically is essential. The study provides a blueprint for conceptualizing and operationalizing ventilation as part of the cooking environment, utilizing both one- and multi-dimensional indicators. Systematizing measurement of ventilation and cooking behaviour can enhance understanding and contribute to more comparable studies in this domain. Relatedly, researchers should be more careful about attributing exposure reductions to changes in technology or ventilation, including behavioural aspects of the latter. Many technology interventions implicitly or explicitly emphasize the harms of cooking emissions, which may lead to differential behaviour change in treated and control populations, confounding the interpretation of the impact estimates from technology alone.

How Could Policy Action Incorporate Ventilation?

The flip side, however, is that policy interventions aimed at improving health might support investment in simple, low-cost ventilation improvements, such as housing modifications that add openings in the kitchen space. Ventilation can also be integrated into interventions that complement clean cooking access policies. For example, information campaigns can sensitize cooks to the many ways they might reduce exposure to harmful smoke and propose tailored solutions to their unique contexts. These may include cooking outdoors, leaving windows and doors open, minimizing time spent in close proximity to the cooking fire, using fans, or installing more advanced solutions such as kitchen retrofits with chimneys and exhaust hoods.

At a more technical level, the study highlights the need to re-evaluate the global default values used to estimate the burden of disease from traditional cooking. A differentiated set of default values that consider fuels, stove cleanliness, and ventilation could provide a more accurate reflection of personal exposure levels, and health consequences.

A Holistic Approach: Beyond Fuels and Stoves

Household air pollution from biomass cooking poses a pressing environmental health risk across the Global South. It remains true that only exclusive use of clean stoves can fully eliminate this pollution. Achieving such exclusive use remains an elusive objective in many contexts, however, and the study’s results challenge the conventional, narrow focus on cooking fuels and stoves in the policy debate on ways to tackle the health harms of household air pollution. A holistic approach that explicitly considers ventilation and related behavioural aspects could lead to more effective intervention planning and policy-making.

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