Q&A: One-third of the total population was exposed to household air pollution in 2021

New research found that in 2021, 2.7 billion people, about one-third of the total population, were exposed to household air pollution. On average, the exposure level when using solid fuel for household cooking was 85 micrograms per cubic meter, which is almost 20 times above the WHO guidelines. We speak with Dr. Katrin Burkhart, Assistant Professor at IHME on what these findings mean for the future of populations around the world who are affected the most.

This transcript has been lightly edited for clarity

What is the research into household air pollution that has just been published?

The study we just published, in it we assessed the global burden of household air pollution. That means the impact of particulate matter that comes from using solid fuels for household cooking.

These fuels can be coal or charcoal. They can be wood. They can be crop residue or dung. Generally, household air pollution is a quite well-established risk factor with a variety of adverse health impacts that are quite well supported with numerous epidemiological studies. The good news is that household air pollution has been declining over the last decades but, especially in low- and middle-income countries, there’s still a large number of the population that relies on these sources for household cooking.

This figure shows us the percentage of population that is exposed to household air pollution. What immediately sticks out in deep red is sub-Saharan Africa. And, in many of the countries, over 90% of the population are exposed to household air pollution. And then there are other countries, such as Sudan, Angola, or Namibia, where the exposure is only between 30% and 50%. In addition to Africa, several countries in South Asia show a quite high percentage of people being exposed to household air pollution as well.

What are the key findings from your research into household air pollution?

So, we found that in 2021, 2.7 billion people, that is about one-third of the total population, were exposed to household air pollution. On average, the exposure level when using solid fuel for household cooking was 85 micrograms per cubic meter, which is almost 20 times above the WHO guidelines.

We also found that about 4% of all disability-adjusted life years could be attributed to household air pollution, and a number of 3.1 million deaths over time; both the total number as well as the rate have been going down by between 35% and 65%. But in areas such as sub-Saharan Africa or South Asia, we still see a really high burden that we can attribute to household air pollution.

In India, the largest country in the region, about 50% of the population are exposed to household air pollution. And then there are some countries, such as Bangladesh or Myanmar, and Laos, where exposures are much higher on average. In East Asia and Latin America and the Caribbean, exposure percentages are more moderate. But then there are countries such as Haiti or North Korea where exposures are really more in line with exposures in sub-Saharan Africa.

What did your research uncover regarding adverse reproductive health outcomes?

So, there is substantial evidence that household air pollution impacts reproductive health outcomes. Babies that are exposed to high particulate matter levels are born earlier or even preterm, and have lower birth weight. Now, at the same time, short gestation and low birth weight can have a multitude of health impacts over the life course.

These range from otitis media to meningitis, encephalitis, sudden infant death syndrome, or other neonatal disorders, as well as diarrheal diseases, or upper and lower respiratory infections. In our study, we accounted for this entire cascade of mediated effects and found that about one-third of the burden that is due to household air pollution can be attributed to these impacts on adverse reproductive health outcomes.

What changes did your research uncover in different fuel types?

This figure shows us the time trends of populations exposed to a specific fuel type, both globally as well as by super-region. Wood is by far the most common fuel type, with declining trends globally and in all the super-regions, especially in South and East Asia.
The second most common fuel type is coal. It is globally declining, which is driven mostly by declines in South Asia but, interestingly, it is increasing in sub-Saharan Africa. Dung and crop residues are generally quite rare, with a slightly higher share in South Asia, and we observe very little change over time.

What factors influenced the changes seen in household air pollution over the last three decades?

This figure shows us the decomposition of different drivers impacting changes in household air pollution attributable burden over the last three decades. Globally, and in all super-regions, we see a negative net percentage change. That is mostly due to the reduction of exposure to household air pollution, which is shown in yellow, and the reduction in other risk factors, which is shown in green.

Population growth and aging, on the other hand, shown in dark and light blue here, are offsetting some of the improvements that have been made on the exposure side.